氮砷化鎵塊材與氮砷化鎵/砷化鎵單一量子井電性與光性的研究

Abstract

本論文主要探討以低壓有機金屬氣相磊晶法成長氮砷化鎵塊材及不同厚度與氮成份的氮砷化鎵/砷化鎵 單一量子井的電性與光性研究。所有樣品成長溫度均為550℃，摻雜矽濃度大約 (1016~1017 cm-3)，氮成份及量子井厚度均由x-ray 繞射模擬求得，其中氮砷化鎵塊材的氮成份是0.9﹪，其它依序是厚度40Å、60 Å、120Å、175 Å、250 Å、295Å與590 Å氮成份是1.8﹪的單一量子井及另一片厚度250 Å氮成分是1.2﹪的量子井。 在電性研究方面，我們使用電容-電壓、導納頻譜、等效電路理論與深層能階暫態來研究樣品導電機制及缺陷能階。從上述量測，可知GaAs0.991N0.009塊材有高阻值特性，室溫下電阻大約3x104 ，並且由導納頻譜量與DLTS量測，推測缺陷能階0.16與0.72eV是造成費米能階被釘(pin)在0.47eV的主因；此外厚度40與60 Å GaAs0.982N0.018 樣品量子侷限很好，可以清楚看到載子被聚集在量子井內，且隨著溫度的上升量子局限現象變弱。再來，厚度250 Å GaAs0.982N0.018樣品，在導納頻譜與DLTS量測，可知存在三個缺陷能階分別為0.34、0.45與0..75eV，其中缺陷能階0.34與0.75eV也被發現在厚度250 Å GaAs0.988N20.012樣品內。此外，缺陷能階0.34eV造成導納量測的電容隨頻率起伏現象，在電容-電壓量測出現高頻載子空乏；低頻載子堆積等現象。對於缺陷能階0.34與0.45eV而言，經由 x-ray rocking curve 與 PL 量測結果可知量子結構良好，所以造成此現象的原因我們推測可能不是晶格鬆弛所造成的缺陷，比較可能是長氮砷化鎵所造成的雜質缺陷或點缺陷造成的影響。此外，我們推測缺陷能階0.75eV是成長砷化鎵所造成的EL2缺陷。此外厚度295Å GaAs0.982N0.018樣品，由DLTS可知造缺陷能階0.49eV是造成載子空乏的主因。

The electrical and optical characteristics of GaAsN bulk and GaAsN/GaAs single quantum wells (SQW) were investigated by varying the GaAsN thickness and Nitrogen composition. The samples were grown by low-pressure Metalorganic Chemical Vapor Deposition (MOCVD) on n+ GaAs (100) substrates. The Nitrogen composition and well thickness were determined from x-ray diffraction patterns. The compositions of nitrogen were 0.9﹪for bulk, 1.2﹪for 250Å SQW and 1.8﹪for 40, 60, 250, 295 and 590Å SQWS. Electrical characteristics were investigated by current-voltage, capacitance-voltage, admittance spectroscopy and deep level transient spectroscopy (DLTS). The GaAs0.991N0.009 bulk sample was shown to be highly resistive with an activation energy of 0.47eV determined from the admittance spectroscopy for its resistance. Two defect levels at 0.16 and 0.72eV were observed by DLTS. Carrier confinement was observed for SQW/GaAs0.982N0.018 samples with thickness of 40 and 60 Å. Carrier depletion was observed for SQW samples with well thickness from 250Å to 590Å. Three traps at 0.34, 0.45 and 0.75eV were found by DLTS and admittance spectroscopy for 250Å SQW/GaAs0.982N0.018. Among the three traps, the traps at 0.34 and 0.75eV were also observed in 250Å SQW/GaAs0.991N0.009 sample. The trap at 0.34eV was shown to be responsible for the carrier accumulation observed in high-frequency measurement and carrier depletion observed in low-frequency measurement around the well region. The trap at 0.75eV was speculated to be EL2 trap. Because of the good quality of the quantum structure shown by PL and x-ray diffraction patterns s, the traps at 0.34 and 0.45eV were speculated to be Nitrogen-related impurities or point defects. For 290 Å SQW GaAs0.982N0.018 sample, the trap at 0.49eV was found to be mainly responsible for the carrier depletion observed in the sample.