氮砷銻化鎵/砷化鎵p-i-n元件特性研究

Abstract

氮砷銻化鎵材料在適當的銻/氮莫爾分率比可有晶格匹配砷化鎵以及能隙低於砷化鎵基板的特性。故此材料是一具有潛力應用砷化鎵基板之上的異質接面電晶體(HBT)或是堆疊式太陽電池的子電池。但是摻入氮會造成塊材材料內部或是異質接面處產生缺陷，使得HBT應用上無法得到高增益，太陽電池應用上無法提高開路電壓。 本篇論文的研究主題使用能隙為1.17-eV之砷化鎵/氮砷銻化鎵在砷化鎵基板上成長異質接面p-i-n元件之特性分析。由不同氮砷銻化鎵厚度(250、500、1000和2000 nm)的元件在不同熱退火條件下的電流電壓特性。未經熱退火製程在順向偏壓中，相同電流密度(0.05 mA/cm2)時電壓隨著厚度的減少而上升0.38至0.46伏特，顯示磊晶的缺陷隨著厚度增加而逐漸產生。經熱退火製程後電流密度變化則不明顯，顯示與元件的厚度無關為表面的復合電流所影響。由飽和電流密度對溫度的關係，我們可求得元件飽和電流密度的活化能，我們發現熱退火後可以讓該活化能趨近能隙，表示表面復合電流下降。熱退火後的的元件經鈍化處理後相同電流密度(0.05 mA/cm2)時電壓會上升50~70 mV，在42倍AM1.5G太陽模擬光源照射時太陽電池轉換效率6.6%

We study the fabrication and the properties of GaAs/GaAs0.97Sb0.02N0.01 heterjunction diodes deposited on GaAs. The energy gap of the GaAs0.97Sb0.02N0.01 layer is 1.17 eV. We found that all the forward currents are higher than the expected p/n junction diffusion current and increases as the GaAs0.97Sb0.02N0.01 layer thickness increases. In addition, the current is proportional to the perimeter instead of the area of the junction, suggesting that it originates from the recombination on the junction surface. From the Arrhenius plot of the saturation current, we found that the activation energy of the as-grown sample is close to half the energy gap of GaAs0.97Sb0.02N0.01, suggesting that the current is a defect recombination current. After thermal annealing, the activation energy increases, indicating the suppression of the surface recombination current. Coating SiN and SiN/SiO2 passivation layers on the junction surface significantly reduces both the reverse and forward currents. The passivated GaAs/ GaAs0.97Sb0.02N0.01 heterjunction shows an optimum conversion efficiency of 6.6% under 42 times of AM1.5G illumination.