熱退火處理之氮離子佈植砷化鎵的缺陷特性

Abstract

我們以電性量測氮離子佈植砷化鎵在不同佈植劑量、不同退火溫度下的特性，發現在高佈植劑量及高退火溫度下樣品呈現高阻植特性。由I-V量測得到未退火樣品缺陷特性以造成穿隧效應為主，經由退火處理後缺陷在樣品□形成再結合中心。由C-V量測得到佈植樣品退火後形成的缺陷分佈是不均勻的。而佈植後基板的載子濃度變小，可能是和氮離子佈植所產生的深階受體（deep acceptor）缺陷產生補償（compensation）效應的結果。由DLTS量測得到高佈植劑量、500℃退火樣品在低溫範圍（100K~250K）內有一broad spectrum （稱為U-band）訊號，由電阻活化能Eact=0.32eV發現此U-band分佈應在0.32 eV附近。由於U-band在高溫退火下消失了，比較x-ray繞射圖的結果，得到U-band是和砷化鎵晶格的膨脹有關。由低佈植劑量（2x1011 cm-2）樣品得到的穩定缺陷能階0.70eV，我們得到氮離子佈植砷化鎵其缺陷能階應該是由淺能階U-band和深能階受體（deep acceptor）缺陷能階所組成的，U-band分佈在0.32 eV附近、而深能階在0.70 eV附近，此缺陷能階和EL2類似。

The nitrogen-implanted GaAs samples after annealing at different temperature have been investigated by secondary ion mass spectroscopy，current-voltage（I-V），capacitance-voltage（C-V），and deep-level transient spectroscopy（DLTS）measurement. The Schottky I-V data show that the conduction of as-implanted samples is dominated by tunneling-assisted defects while the conduction after annealing is governed mainly by generation-recombination centers. The layer implanted with high nitrogen dose（2x1015 cm-2）is shown to be highly resistive after annealing. The concentration of nitrogen-implanted GaAs is found to be compensated by non-uniformly distributed acceptors. The DLTS measurement shows a broad spectrum（called U-band）in the low temperature range of 100 to 250K in highly N-implanted sample after annealing at 500℃. In terms of the activation energy of the resistance，the U-band should be around 0.32eV below the minimum of the conduction band. Since the U-band can be annealed out at higher temperature，it is associated to the lattice-expansion defect peak observed in the x-ray spectrum. Based on the experimental data，we conclude that the nitrogen implantation in GaAs can introduce defects consisting of the U-band around 0.32eV and a deep acceptor around 0.7eV.