重摻雜碳的GaAsBi霍爾效應及光致發光特性分析

Abstract

本研究針對重摻雜碳的鉍砷化鎵(GaAsBi)樣品進行霍爾量測與光致發光(PL)特性分析，以探討其電性與光學行為，重摻雜碳的樣品摻雜濃度約在4×10^18(cm)^(-3)至6×10^19(cm)^(-3)的範圍內，另有一片無摻雜樣品載子濃度為3.7×10^17(cm)^(-3)。霍爾量測結果顯示所有樣品均呈p型導電性，且載子遷移率會隨TMBi flow及載子濃度的增加而提升。PL量測確認GaAs摻雜了Bi可有效縮減能隙，使得光譜中出現低於GaAs能隙之能量的波峰。進一步分析光譜，發現較高載子濃度的樣品多半具有雙波峰結構，而較低的載子濃度似乎較不容易出現雙波峰結構。後續針對有觀察到雙波峰的PL光譜進行雙高斯擬合，分析出高能量波峰對溫度變化不敏感，而低能量波峰則具溫度依賴性。本研究認為雙波峰的成因有兩種可能：第一種可能是高濃度摻雜導致雜質能帶(impurity band)產生，使光復合路徑除了有典型的band-to-band以外，還額外多出了band-to-impurity band的路徑，這兩種光復合路徑會分別產生高能量及低能量波峰。第二種可能為波向量不守恆，由於高濃度摻雜會在價帶額外注入許多電洞，使電洞分布的範圍不限於價帶頂部，還會擴及價帶下層，增加波向量不守恆發生的機率，當波向量守恆與波向量不守恆的光復合機制同時存在時，便會產生低能量及高能量波峰，使光譜上出現雙波峰結構。

This study investigates the electrical and optical properties of gallium arsenide bismide (GaAsBi) samples subjected to heavy carbon doping. Hall effect and photoluminescence (PL) measurements were performed to analyze carrier behavior and band structure characteristics. Seven samples were heavily doped with carbon, with doping concentrations ranging from approximately 4×10^18 (cm)^(-3) to 6×10^19(cm)^(-3), while one undoped sample exhibited a background concentration of 3.7×10^17(cm)^(-3). Hall measurements confirmed that all samples exhibit p-type conductivity, and the hole mobility increases with higher TMBi and carbon flow rates. PL measurements revealed that bismuth incorporation effectively reduces the bandgap of GaAs, resulting in emission peaks at energies lower than the intrinsic GaAs bandgap. Further spectral analysis showed that samples with higher carrier concentrations tend to exhibit a dual-peak structure in their PL spectra, whereas samples with lower carrier concentrations are less likely to display such features. To investigate the origin of the dual peaks, dual-Gaussian fitting was applied to the PL spectra. The results indicate that the high-energy peak is relatively insensitive to temperature changes, while the low-energy peak exhibits strong temperature dependence. Two mechanisms are proposed to explain this phenomenon. The first involves the formation of impurity bands due to heavy doping, which introduces an additional radiative recombination pathway band-to-impurity band alongside the conventional band-to-band transition. These two pathways correspond to the high- and low-energy peaks, respectively. The second mechanism is attributed to wave vector non-conservation. Heavy doping introduces a large number of holes into the valence band, expanding their distribution beyond the band edge and into deeper energy levels. This increases the likelihood of non-conserving transitions. When both conserving and non-conserving recombination mechanisms coexist, they give rise to distinct high- and low-energy peaks, resulting in the observed dual-peak structure in the PL spectra.