本研究は、文部科学省の日本学術振興会(JSPS)科研費(17J10044)の助成を受けて行われました。製造プロセスは、文部科学省の「ナノテクノロジープラットフォーム」(プロジェクト番号12024046)によってサポートされました。著者らは、東京大学の山下和彦氏と平田聡氏のTEM観測に協力してくださったことに感謝する。

1. 理論計算手順
<ol><li>TDの軌道を計算します。計算では、SEGマスクがTDD低減に対するART効果を無視するのに十分なほど薄いと仮定します。<ol><li>成長面を決定し、方程式で表します。たとえば、補足ビデオ1aおよび式(1)に示すように、SEG Ge層の丸い断面の時間発展を、時間発展パラメータn = i、SEG Geの高さ(hi)、およびSEG Ge半径(ri)で表します。 <img alt="Equation 4" src="/files/ftp_upload/58897/58897eq4.jpg" style="opacity: 0.9;"></li>
		<li>成長サーフェス上の任意の位置の法線方向を決定します。丸型断面SEG Geについては、補足動画1bに赤線で示す(xi,yi)<img alt="Equation 7" src="/files/ftp_upload/58897/58897eq7v2.jpg" style="opacity: 0.9;">の法線を次のように記述する。次に、次の連立方程式を解いて、点(xi、y i)からTDのエッジ(x i + 1、y i + 1)を取得します。 <img alt="Equation 10" src="/files/ftp_upload/58897/58897eq10.jpg" style="opacity: 0.9;"></li>
		<li>補足ビデオ 1c に示すように、TD 生成の場所 (x 0, 0) に応じて 1 TD の軌道を計算します。つまり、任意のTDの軌跡は、上述の方法により算出することができる。</li>
		<li>TDが底面に浸透し、TDDの減少に寄与すると仮定してTDDを計算します(つまり、SEG Ge層が合体するポイントより下のTDは半円筒形のボイドに閉じ込められ、上面に現れません)。</li>
	</ol></li>
</ol>2. 実験検証手順
<ol><li>SEGマスクの準備<ol><li>SEGマスクを作製する前に、設計ファイルを準備してGe成長領域を定義します。本研究では、市販のソフトウェア(AutoCADなど)を用いて、[110]方向と幅4mmの正方形状のSi窓領域に整列したラインアンドスペースパターンを準備します。</li>
		<li>ソフトウェアを使用してSEGマスク(特にWウィンドウとWマスク)の設計を決定します。Wウィンドウはウィンドウ幅(Siシード幅)、WマスクはSiO2マスク幅であり、SEG Ge層が隣接する層と合体できるようにします。WウィンドウとWマスクを決定するには、[ファイル→構造を開く]をクリックして長方形を描画し→長方形またはポリラインをクリックします。 注:長方形の幅はWウィンドウになり、長方形の間隔はWマスクになります。本研究では、Wウィンドウ とWマスク の最小値はそれぞれ0.5 μmと0.3 μmであり、採用しているEBリソグラフィシステムの分解能によって制限されています。</li>
		<li>参考として、ブランケット領域とみなす幅D4mmの正方形のSi窓領域を描く。[ ファイル→構造を四角形またはポリライン→開く ]をクリックして、正方形のSiウィンドウを描画します。図1に示す回路 図 を使用して、ラインアンドスペースパターンと4mm四方のブランケット領域を準備します。</li>
		<li>抵抗率が1〜100 Ω・cmのBドープp-Si(001)基板を準備します。本研究では、4インチのSi基板を使用します。必要に応じて、ピラニア溶液(20mLの30%H 2 O 2と80 mLの96%H 2SO4の混合物)で基板表面を洗浄します。</li>
		<li>管状炉の蓋を開け、ガラス棒を使用してSi基板を炉に装填します。本研究では、一度に10枚のSi基板を酸化します。</li>
		<li>ガスバルブを開いて乾燥N2 ガスを炉内に吹き込み始める。次に、バルブを制御してガス流量を0.5 L / mに設定します。</li>
		<li>プログラムを変更して焼鈍温度を設定します。本作業では、「パターン工程(モード2)」を使用し、工程温度を900°Cに設定する。 次に、関数を押してプログラムを実行し →実行します。</li>
		<li>温度が900°Cに達したら、ドライN 2バルブを閉じ、ドライO 2バルブ(O 2フロー= 1 L / m)を開き、2時間保持します。 注意: 黄色の部屋で手順2.1.9〜2.1.16を実行します。</li>
		<li>酸化したSi基板をスピンコーターを用いて界面活性剤(OAP)でコーティングし、ホットプレート上で110°Cで90秒間ベークします。</li>
		<li>界面活性剤塗布後、スピンコーターを用いてSi基板をフォトレジスト(ZEP520Aなど)で塗布し、ホットプレート上で180°Cで5分間ベークします。</li>
		<li>界面活性剤とフォトレジストを含むSi基板を電子ビーム(EB)ライターにロードします。</li>
		<li>EBライターで設計ファイル(手順2.1.2で用意)を読み込み、オペレーションファイル(WECファイル)を作成します。WECファイルで線量量を120μC/cm2 に設定します。基板の装填が終了したら、 単回 露光ボタンをクリックしてEB露光を行います。</li>
		<li>露光が終了したら、 ウェーハキャリー→アンロード をクリックして、EBライターから基板をアンロードします。</li>
		<li>ドラフトチャンバーでフォトレジスト現像液(ZED)と現像液用リンス液(ZMD)を準備します。露出したSi基板を現像液に室温で60秒間浸します。</li>
		<li>現像液からSi基板を取り出し、N2 ガスで基板を乾燥させます。</li>
		<li>現像したSi基板をホットプレートに載せ、110°Cで90秒間ベークします。</li>
		<li>Si基板を緩衝フッ化水素酸(BHF-63SE)に1分間浸して、EB曝露および現像の結果として空気にさらされたSiO2 層の一部を除去します。</li>
		<li>有機フォトレジスト除去剤(Hakuri-104など)に15分間浸漬して、Si基板からフォトレジストを除去します。</li>
		<li>Si基板を0.5%希フッ化水素酸に4分間浸して、窓領域の薄い自然酸化物を除去しますが、SiO2 マスクを保持します。次に、超高真空化学気相成長(UHV-CVD)チャンバーにロードしてGeを成長させます。 図2 に本研究で用いたUHV-CVDシステムを示す。</li>
	</ol></li>
	<li>エピタキシャルGe成長<ol><li>SEGマスク(ステップ2.1のように作製)を備えたSi基板をロードロックチャンバーにロードします。</li>
		<li>バッファー/主成長温度は、オペレーションコンピュータに表示される レシピ タブで設定します。SEG Ge層が隣接する層と合体するように、Geの主な成長の期間を決定します。主な成長の期間を決定するために、面内/横方向の成長を決定する{113}面上のGeの成長率を考慮してください26。本研究では、主成長の持続時間を650°Cと700°Cでそれぞれ270分と150分に設定します。</li>
		<li>メインウィンドウで 開始 をクリックすると、Si基板が自動的に成長チャンバーに転送されます。 注:エピタキシャルGe成長に関するプロトコル(ステップ2.2.4-2.2.7)は自動的に処理されます。</li>
		<li>装填したSi基板上にGeバッファーを低温(≈380°C)で成長させる。原料ガスとしてArで9%に希釈したGeH4を使用し、バッファー成長中はGeH4の分圧を0.5Paに保つ。</li>
		<li>高温でGeメイン層を成長させます。主成長中はGeH4 の分圧を0.8 Paに保ちます。本研究では、SEG Geを円形の断面と{113}面の断面25と比較するために、主成長温度に650°Cと700°Cの2つの異なる温度を使用します。 注:(001)面でのGeの成長速度は、温度とは無関係に11.7 nm / minでした。</li>
		<li>SEG Geの進化とその合体を可視化するために、別のSi基板上に厚さ10nmのSi0.3Ge0.7境界層を周期的に挿入しながらGe成長を行います。Si0.3 Ge 0.7層は、Si2H6およびGeH4ガスを用いて形成した。Si0.3Ge0.7層成長中は、Si2H6ガスの分圧を0.02Pa、GeH4ガスの分圧を0.8Paとする。</li>
		<li>Si基板は成長チャンバーからロードロックチャンバーに自動的に転送されるため、ロードロックチャンバーをベントし、Si基板を手動でアンロードします。</li>
	</ol></li>
	<li>エッチングピット密度(EPD)測定<ol><li>超音波洗浄機を用いて、32mgのI2 を67mLのCH3COOHに溶解する。</li>
		<li>I2-溶解したCH3COOH、20mLのHNO3、および10mLのHFを混合する。</li>
		<li>Ge成長したSi基板をCH3COOH / HNO3 / HF / I2 溶液に5〜7秒間浸して、エッチングピットを形成します。</li>
		<li>エッチングされたGe表面を光学顕微鏡(通常は100倍)で観察し、エッチングされたピットが正常に形成されていることを確認します。</li>
		<li>原子間力顕微鏡(AFM)を使用して、エッチングされたピットをカウントします。エッチングしたGeサンプルをAFMステージに置き、自動 アプローチをクリックしてプローブに近づきます。</li>
		<li>AFMと一体化した光学顕微鏡で観察エリアを決め、10μm×10μmの5つのエリアをスキャンします。振幅減衰係数は自動的に決定されます。</li>
	</ol></li>
	<li>電子顕微鏡観察<ol><li>集束Geイオンビーム(FIBマイクロサンプリング法)を使用して、合体/ブランケットGe層からTEM試料をピックアップします27。</li>
		<li>TeM試料をArイオンを用いたイオンミリングシステムで研磨します。本研究では、断面観察では[110]方向に150-500 nm、平面観察では[001]方向に200 nmとするTEM試料を薄くする。</li>
		<li>平面TEM試料の場合は、Ge層の上面をアモルファス層で保護し、Ge層の下(基板)側から薄くします。</li>
		<li>加速電圧200kVでTEM観察を行います。厚い(500 nm)TEM試料を観察するために、断面明視野走査TEM(STEM)観察を実行します。</li>
		<li>Si0.3 Ge 0.7境界層と合体したGeの場合、加速電圧200 kVで断面高角環状暗視野(HAADF)STEM観測を行います。</li>
	</ol></li>
</ol>

著者は開示するものは何もありません。

本研究では、4 x 107 / cm2 のTDDが実験的に示されました。さらなるTDD低減のために、プロトコル内には主にSEGマスク調製とエピタキシャルGe成長の2つの重要なステップがあります。
図4に示す我々のモデルは、APR、Wウィンドウ/(Wウィンドウ+ Wマスク)が0.1と小さい場合、合体GeでTDDを107/cm2未満に減らすこ...

Si上のエピタキシャルGeは、光通信範囲(1.3〜1.6μm)の光を検出/放出でき、Si CMOS(相補型金属酸化膜半導体)処理技術に適合するため、アクティブフォトニックデバイスプラットフォームとして大きな関心を集めています。しかし、GeとSiの格子不整合は4.2%と大きいため、Si上のGeエピタキシャル層では~109/cm2の密度でねじ切り転位(TD)が形成されます。Geフォトニックデバイスは、TDがGe光検出器(PD)や変調器(MOD)のキャリア生成センターとして、レーザーダイオード(LD)のキャリア再結合センターとして機能するため、TDによって性能が低下します。次に、PDおよびMOD1,2,3の逆リーク電流(Jリーク)とLD4,5,6のスレッショルド電流(Jth)を増加させます。
Si上のGeのTD密度(TDD)を低下させるための様々な試みが報告されている(補足図1)。熱アニーリングはTDの動きを刺激し、TDDを典型的には2 x 107 / cm2に減少させます。欠点は、SiとGeの混合と、リン7,8,9などのGe中のドーパントのアウトディフュージョンの可能性です(補足図1a)。SiGe傾斜バッファ層10,11,12は、臨界厚さを増加させ、TDDの生成を抑制し、TDDを典型的には2 x 106/cm2に減少させる。ここでの欠点は、バッファが厚いため、Geデバイスとその下のSi導波路との間の光結合効率が低下することです(補足図1b)。アスペクト比トラップ(ART)13,14,15は選択的エピタキシャル成長(SEG)法であり、厚いSiO 2トレンチの側壁にTDをトラップすることにより、TDを通常<1 x 10 6 / cm2に低減します。ART法では、厚いSiO 2マスクを使用して、Siのはるか上に位置し、同じ欠点を持つSiO2マスクよりもGeのTDDを低減します(補足図1b、1c)。Siピラーシード上のGe成長とアニーリング16,17,18はART法と同様であり、高アスペクト比Ge成長によるTDトラップを可能にし、<1 x 105 / cm2になります。しかしながら、Ge合一のための高温アニールは、補足図1a〜c(補足図1d)において同じ欠点を有する。
上記の方法の欠点のないSi上で低TDDのGeエピタキシャル成長を達成するために、これまでにSEGGe成長7,15,21,22,23で報告された次の2つの重要な観察結果に基づいて、合体誘起TDD低減19,20を提案しました。:1)TDは成長面に垂直になるように曲げられ(断面透過型電子顕微鏡(TEM)によって観察され)、2)SEG Ge層の合体により、SiO2マスク上に半円筒形の空隙が形成されます。
TDは成長面からのイメージ力によって曲がっていると仮定しました。Si上のGeの場合、イメージ力は、自由表面から1nm離れた距離でのねじ転位とエッジ転位に対してそれぞれ1.38GPaと1.86GPaのせん断応力を生成します19。計算されたせん断応力は、Ge24の60°転位について報告された0.5GPaのパイエルス応力よりも大幅に大きい。この計算は、定量的にGe SEG層のTDD減少を予測し、SEG Geの成長19とよく一致しています。TDのTEM観測は、Si20上で提示されたSEG Ge成長におけるTD挙動を理解するために行われる。画像力誘起TDD低減は、熱アニーリングや厚いバッファ層がないため、フォトニックデバイスアプリケーションに適しています。
本稿では、TDD低減法の提案に採用されている理論計算と実験的検証の具体的手法について述べる。

<table border="0" cellpadding="0" cellspacing="0" style="width:655px;" width="656">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:222px;">AFM</td>
			<td style="width:140px;">SII NanoTechnology</td>
			<td style="width:123px;">SPI-3800N</td>
			<td style="width:171px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BHF</td>
			<td>DAIKIN</td>
			<td>BHF-63U</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CAD design</td>
			<td>AUTODESK</td>
			<td>AutoCAD 2013</td>
			<td>Software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CH3COOH</td>
			<td>Kanto-Kagaku</td>
			<td>Acetic Acid</td>
			<td>for Electronics</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CVD</td>
			<td>Canon ANELVA</td>
			<td>I-2100 SRE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Developer</td>
			<td>ZEON</td>
			<td>ZED</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Developer rinse</td>
			<td>ZEON</td>
			<td style="width:123px;">ZMD</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EB writer</td>
			<td>ADVANTEST</td>
			<td>F5112+VD01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Furnace</td>
			<td>Koyo Thermo System</td>
			<td>KTF-050N-PA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HF, 0.5 %</td>
			<td>Kanto-Kagaku</td>
			<td>0.5 % HF</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HF, 50 %</td>
			<td>Kanto-Kagaku</td>
			<td>50 % HF</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HNO3, 61 %</td>
			<td>Kanto-Kagaku</td>
			<td>HNO3 1.38</td>
			<td>for Electronics</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">I2</td>
			<td>Kanto-Kagaku</td>
			<td>Iodine 100g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Photoresist</td>
			<td>ZEON</td>
			<td>ZEP520A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Photoresist remover</td>
			<td>Tokyo Ohka</td>
			<td>Hakuri-104</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Surfactant</td>
			<td>Tokyo Ohka</td>
			<td>OAP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TEM</td>
			<td>JEOL</td>
			<td>JEM-2010HC</td>
			<td></td>
		</tr>
	</tbody>
</table>

theoretical calculation and experimental verification for dislocation reduction in germanium epitaxial layers with semicylindrical voids on silicon

シリコン(Si)上のエピタキシャルゲルマニウム(Ge)のねじ切り転位密度(TDD)の低減は、モノリシックに統合されたフォトニクス回路の実現にとって最も重要な課題の1つです。本稿では,TDD低減のための新規モデルの理論計算方法と実験的検証の手法について述べる.理論計算方法は、転位像力の観点から、選択的エピタキシャル成長(SEG)のTDと非平面成長面の相互作用に基づくねじ切り転位(TD)の曲げを記述します。計算は、SiO2 マスク上のボイドの存在がTDDの減少に役立つことを明らかにしています。実験的検証は、超高真空化学気相成長法を用いたゲルマニウム(Ge)SEGによる、エッチングおよび断面透過型電子顕微鏡(TEM)による成長したGeのTD観察によって記述される。TDDの減少は、SiO2 SEGマスク上の半円筒空隙の存在と成長温度によるものであることが強く示唆されています。実験的検証のために、半円筒形のボイドを有するエピタキシャルGe層が、Ge層のSEGおよびそれらの合体の結果として形成される。実験的に得られたTDDは、理論モデルに基づいて計算されたTDDを再現します。断面TEM観察により、TDの終端と生成の両方が半円筒形の空隙で発生することが明らかになりました。平面図TEM観察により、半円筒形のボイドを持つGe中のTDのユニークな挙動が明らかになりました(つまり、TDはSEGマスクとSi基板に平行になるように曲がっています)。

理論計算
図3は、6種類の合体Ge層におけるTDの計算軌跡を示しています。 ここでは、開口率(APR)をWウィンドウ/(Wウィンドウ+Wマスク)と定義します。図3aは、APR=0.8のGeが合体した丸型SEG原点を示す。ここでは、2/6TDがトラップされています。<str...

Watch this Scientific Journal Video about Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon at JoVE.co

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

シリコン上に半円筒空隙を有するゲルマニウムエピタキシャル層におけるねじ切り転位(TD)密度の低減について、理論計算と実験的検証が提案されています。像力によるTDと表面の相互作用に基づく計算、TD測定、TDの透過型電子顕微鏡観察を示します。

シリコン上に半円筒空隙を有するゲルマニウムエピタキシャル層の転位低減に関する理論計算と実験的検証

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the ...

theoretical-calculation-experimental-verification-for-dislocation

Research

JoVE Journal

Engineering

2.1K ビュー.  The University of Tokyo. シリコン上に半円筒空隙を有するゲルマニウムエピタキシャル層におけるねじ切り転位(TD)密度の低減について、理論計算と実験的検証が提案されています。像力によるTDと表面の相互作用に基づく計算、TD測定、TDの透過型電子顕微鏡観察を示します。 

ビデオ: Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach.
The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles.
To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 &mu;m thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint.
To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23&deg;C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only.
Introduction
Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested.
Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10.
The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only.

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

プラズモニック·強化されたライトトラップによる多結晶シリコン薄膜太陽電池

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To ...

工学

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

液体環境におけるパルスUVレーザー照射によるシリコン表面の濡れ性の選択エリア変更

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

転写印刷により水素化微結晶シリコン太陽電池の光トラッピング銀ナノ構造の統合

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

核反応分析と深さ方向分析を通じて表面・界面層とバルク材料中の水素濃度の定量

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

SSVEP-based Experimental Procedure for Brain-Robot Interaction with Humanoid Robots

Brain-Robot Interaction (BRI), which provides an innovative communication pathway between human and a robotic device via brain signals, is prospective in helping the disabled in their daily lives. The overall goal of our method is to establish an SSVEP-based experimental procedure by integrating multiple software programs, such as OpenViBE, Choregraph, and Central software as well as user developed programs written in C++ and MATLAB, to enable the study of brain-robot interaction with humanoid robots.
This is achieved by first placing EEG electrodes on a human subject to measure the brain responses through an EEG data acquisition system. A user interface is used to elicit SSVEP responses and to display video feedback in the closed-loop control experiments. The second step is to record the EEG signals of first-time subjects, to analyze their SSVEP features offline, and to train the classifier for each subject. Next, the Online Signal Processor and the Robot Controller are configured for the online control of a humanoid robot. As the final step, the subject completes three specific closed-loop control experiments within different environments to evaluate the brain-robot interaction performance.
The advantage of this approach is its reliability and flexibility because it is developed by integrating multiple software programs. The results show that using this approach, the subject is capable of interacting with the humanoid robot via brain signals. This allows the mind-controlled humanoid robot to perform typical tasks that are popular in robotic research and are helpful in assisting the disabled.

The overall goal of this method is to establish an SSVEP-based experimental procedure by integrating multiple software programs to enable the study of brain-robot interaction with humanoid robots, which is prospective in assisting the sick and elderly as well as performing unsanitary or dangerous jobs.

ヒューマノイドロボットと脳とロボットのインタラクションのための実験手順をSSVEPベース

Brain-Robot Interaction (BRI), which provides an innovative communication pathway between human and a robotic device via brain signals, is prospective in ...

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

The goal of this protocol is to present how to perform spin- and angle-resolved photoemission spectroscopy combined with polarization-variable 7-eV laser (laser-SARPES), and demonstrate a power of this technique for studying solid state physics. Laser-SARPES achieves two great capabilities. Firstly, by examining orbital selection rule of linearly polarized lasers, orbital selective excitation can be carried out in SAPRES experiment. Secondly, the technique can show full information of a variation of the spin quantum axis as a function of the light polarization. To demonstrate the power of the collaboration of these capabilities in laser-SARPES, we apply this technique for the investigations of spin-orbit coupled surface states of Bi2Se3. This technique affords to decompose spin and orbital components from the spin-orbit coupled wavefunctions. Moreover, as a representative advantage of using the direct spin detection collaborated with the polarization-variable laser, the technique unambiguously visualizes the light polarization dependence of the spin quantum axis in three-dimension. Laser-SARPES dramatically increases a capability of photoemission technique.

Here, we combine polarization-variable 7-eV laser with spin- and angle-resolved photoemission technique to visualize the spin-orbital coupling effect in solid states.

偏波可変レーザーと組み合わせてスピン角度分解光電子分光の実験法

The goal of this protocol is to present how to perform spin- and angle-resolved photoemission spectroscopy combined with polarization-variable 7-eV laser ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

Ex その場その場で調査構造変換の方法: 金属ガラスの結晶化の事例

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

A protocol for the fabrication of magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for transmission electron microscopy (TEM) and magnetic transmission x-ray microscopy (MTXM) studies is presented.

磁気渦の研究伝達顕微鏡検査の技術を使用してシリコン窒化膜の磁性ナノ構造の作製

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared ...

A Silicon-tipped Fiber-optic Sensing Platform with High Resolution and Fast Response

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This FOSP relies on a silicon Fabry-Perot interferometer (FPI) attached to the fiber end, referred to as Si-FOSP in this work. The Si-FOSP generates an interferogram determined by the optical path length (OPL) of the silicon cavity. Measurand alters the OPL and thus shifts the interferogram. Due to the unique optical and thermal properties of the silicon material, this Si-FOSP exhibits an advantageous performance in terms of sensitivity and speed. Furthermore, the mature silicon fabrication industry endows the Si-FOSP with excellent reproducibility and low cost toward practical applications. Depending on the specific applications, either a low-finesse or high-finesse version will be utilized, and two different data demodulation methods will be adopted accordingly. Detailed protocols for fabricating both versions of the Si-FOSP will be provided. Three representative applications and their according results will be shown. The first one is a prototype underwater thermometer for profiling the ocean thermoclines, the second one is a flow meter to measure flow speed in the ocean, and the last one is a bolometer used for monitoring exhaust radiation from magnetically confined high-temperature plasma.

This work reports an innovative silicon-tipped fiber-optic sensing platform (Si-FOSP) for high-resolution and fast-response measurement of a variety of physical parameters, such as temperature, flow, and radiation. Applications of this Si-FOSP span from oceanographic research, mechanical industry, to fusion energy research.

高解像度・高速応答の光ファイバーセンシングのシリコン チップを渡したプラットフォーム

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This ...