Ga_xIn_<1-x>As多結晶薄膜の電気的光学的特性(窒化物及び混晶半導体デバイス)  [in Japanese] Electrical and optical properties of polycrystalline Ga_xIn_<1-x>As thin films  [in Japanese]

分子線蒸着法によりガラス基板上に基板温度240℃及び350℃でGa組成x=0〜1のGa_xIn_<1-x>As多結晶を約1μm成長させた.100〜390Kでのホール効果測定の結果,電子濃度は,x≦0.30の試料では測定温度にほとんど依存しなかったが,x≧0.36の試料では測定温度の低下とともに減少した.電子移動度も,Ga組成x≦0.21の試料では測定温度にほとんど依存しなかったが,x≧0.3の試料では測定温度の低下とともに減少した.電子濃度の温度依存性は2種類のドナー準位が存在するとして説明され,電子移動度の温度依存性は粒界障壁をこえる熱電子放出によって説明される.また,透過スペクトルを測定し,吸収係数と光学的バンドギャップを求めた.x≦0.44の試料に対してはBurstein-Mossシフトを考慮し,x≦0.30の試料に対しては粒界障壁による量子閉じ込め効果を考慮することにより,光学的バンドギャップのGa組成依存性が説明できた.

Polycrystalline Ga_xIn_<1-x>As films having Ga contents of x=0-1 and the thickness of about 1μm were grown on glass substrates at 240 and 350℃ by molecular-beam deposition. Hall-effect measurements at 100-390K revealed that the electron concentration of the samples having Ga contents of x≦0.30 was almost independent of the measurement temperature, while that of the samples having x≧0.36 decreased with decreasing temperature. The electron mobility of the samples having Ga contents of x≦0.21 was almost independent of the measurement temperature, while that of the samples having x≧0.30 decreased with decreasing temperature. The temperature dependence of electron concentration is explained assuming the existence of two donor levels. The temperature dependence of electron mobility is explained in terms of thermionic electron emission over the grain-boundary barriers. In addition, optical transmission measurements were performed in order to investigate the absorption coefficient and the optical band gap. The dependence of the optical band gap on the Ga content can be explained by taking into account the Burstein-Moss shift for samples having x≦0.44, and the quantum confinement effect due to the grain-boundary barriers for the samples having x≦0.30.