GaAsBi / GaAs奈米結構的成長與特性分析

Abstract

我們在半絕緣偏斜角為±0.1°砷化鎵(001)基板，半絕緣偏斜角為±0.1°砷化鎵(111)A基板上用分子束磊晶法成長了GaAs buffer和GaAsBi薄膜，這層buffer我們以1μm/h的速率成長，成長溫度落在650℃，As2/Ga BEP維持在6。而在磊晶層的部分，我們以0.33μm/h的速率成長，將As2/Ga的BEP比從3逐漸調整至2，Bi/Ga 的BEP比從0.084逐漸調整至0.12，並逐漸降低長晶溫度。 對於(111)A基板的樣品，我們使用SEM在樣品上觀察到了奈米線(NWs)的出現，我們通過EDX的結果和僅成長buffer的樣品確定了奈米線為純GaAsBi的材料而非core shell的結構，也排除了Vapor-Liquid-Solid的生長機制。根據成長條件我們找到了最適合GaAsBi NW成長的growth window，我們發現最佳生長溫度為300°C，As2/Ga BEP比率為2且Bi/Ga BEP比率範圍在0.1-0.12之間時有助於奈米線的成長。我們獲得了具有1:10縱橫比的砷化鎵鉍奈米線。此外，通過 TED 分析，我們在奈米線的頂部發現了twinning的存在。 對於(001)基板的樣品，我們使用了HRXRD、SEM、EPMA和RSM這些儀器和技術進行量測。我們先用HRXRD的結果判斷磊晶品質，再用SEM確定樣品表面是否有液滴，鉍的組成則通過電子探針微區分析和倒置空間映射進行了分析，從RSM的結果也得到了磊晶層的relaxation。我們樣品大部分的砷化鎵鉍層是鬆弛的。 從測量結果來看，降低生長溫度對磊晶層中鉍含量的影響似乎並不顯著，但這一改變可以有效降低磊晶層的弛豫程度。在低溫生長條件下，我們觀察到鉍原子的粘附係數接近1。僅提升Bi/Ga的BEP比例，我們的樣品中鉍含量也會線性的增加而不受其他條件影響。同時，較高的鉍含量也會導致更高弛豫程度。然而在僅降低As2/Ga的BEP Ratio的樣品中，降低As2/Ga BEP比率能夠顯著降低Relaxation的程度。然而，隨著As量的減少，Relaxation的降低幅度也會逐漸變小。

We grew GaAs buffer and GaAsBi films on semi-insulating GaAs (001) and GaAs (111)A substrates with a misorientation angle of ±0.1° using molecular beam epitaxy (MBE). The buffer layer was grown at a rate of 1 μm/h at a temperature of 650°C, with an As2/Ga BEP ratio maintained at 6. For the epitaxial layer, we grew it at a rate of 0.33 μm/h, gradually adjusting the As2/Ga BEP ratio from 3 to 2 and the Bi/Ga BEP ratio from 0.084 to 0.12, while gradually lowering the growth temperature. For the samples on the (111)A substrate, we observed the formation of nanowires (NWs) using SEM. EDX results and samples with only the buffer layer confirmed that the nanowires were made of pure GaAsBi material rather than a core-shell structure, and we ruled out the Vapor-Liquid-Solid growth mechanism. Based on growth conditions, we identified the optimal growth window for GaAsBi NWs. We found that the best growth temperature was 300°C, with an As2/Ga BEP ratio of 2 and a Bi/Ga BEP ratio range of 0.1-0.12, which facilitated NW growth. We obtained GaAsBi nanowires with an aspect ratio of 1:10. Additionally, TED analysis revealed the presence of twinning at the tops of the NWs. For the samples on the (001) substrate, we used HRXRD, SEM, EPMA, and RSM for measurements. We assessed the epitaxial quality using HRXRD results, confirmed the presence of droplets on the sample surface using SEM, and analyzed the bismuth composition through EPMA and reciprocal space mapping (RSM), which also revealed the relaxation of the epitaxial layer. Most of the GaAsBi layers in our samples were relaxed. Our measurement results indicate that lowering the growth temperature does not significantly affect the bismuth content in the epitaxial layer, but it effectively reduces the relaxation degree of the epitaxial layer. Under low-temperature growth conditions, we observed that the sticking coefficient of bismuth atoms approached 1. By only increasing the Bi/Ga BEP ratio, the bismuth content in our samples increased linearly without being affected by other conditions. However, higher bismuth content also led to higher relaxation. In samples where only the As2/Ga BEP ratio was decreased, lowering the As2/Ga BEP ratio significantly reduced the degree of relaxation. However, as the arsenic amount decreased, the reduction in relaxation also gradually diminished.