電子-聲振子散射之自由載子吸收在準一維量子結構內之效應

Abstract

半導體中自由載子吸收的量子理論之研究已經延伸到如細量子線之自由載子侷限的準一維量子結構，由於載子的受限制，其在準一維量子結構移動的能量就被量子化了。本文研討由N型砷化鎵半導體製造之準一維量子結構，其自由載子吸收之量子理論，是經由載子與光頻聲子或聲頻聲子之散射所引起的。我們假設半導體內之電子能帶為非拋物線型，考慮的散射機構為 [a]電子－極化光頻聲子的散射，[b]電子－聲頻聲子的散射，及 [c]在Ⅲ-Ⅴ族化合物半導體的壓電散射。若散射由聲頻聲子所引起時，則形變位能耦合或壓電耦合為其主要散射機構。最後數值分析結果顯示，在N型砷化鎵半導體內自由載子吸收係數依散射機構形態、光子頻率、橫向尺度及操作溫度而變化。

The quantum theory of free-carrier absorption in semiconductors is extended to treat the case where the free carriers are confined in quasi-one-dimensional semiconducting structures such as ultrathin quantum wires. As a result of the confinement of the carriers, the energy of the motion of carriers in quasi-one-dimensional structures is size quantized. The free-carrier absorption in these low-dimensional structures fabricated from n-type GaAs has been investigated for the case where the carriers are scattered either by polar optical phonons or acoustic phonons. The energy band of electrons in semiconductors is assumed to be nonparabolic. The scattering mechanisms of the interaction between electrons and phonons we consider here come from [a] electron-polar-optical-phonon scattering, [b] electron-acoustic-phonon scattering, and [c] piezoelectric scattering in III-V compound semiconductors. When the carriers in quasi-one-dimensional semiconducting structures are scattered by the acoustic phonons, the effect of acoustic phonon scattering on the free-carrier absorption coefficient for both deformation-potential coupling and piezoelectric coupling in III-V compound semiconductors are considered. Results show that the free-carrier absorption coefficient in n-type GaAs depends on the scattering types of phonons, photon frequency, transverse dimensions, and operation temperature.