磷化鋁鎵銦材料成長、製程與缺陷分析

Abstract

磷化鋁鎵銦材料可成長於砷化鎵基板上，改變材料中的鋁鎵比率，可改變材料直接能隙由1.9電子伏特變為2.23電子伏特，因此可用於製作量子井結構，進而用於太陽能電池、紅光雷射及高亮度發光二極體等光電元件上。然而材料成長過程，或是摻雜行為，乃至後續製程的處理，均有可能造成材料中的缺陷形成復合中心，進而影響元件的特性。本論文主要將有機金屬化學氣象磊晶法成長磷化鋁鎵銦材料，並針對上述幾點可能造成材料缺陷的問題，以深層缺陷暫態頻譜分析儀對材料加以分析，嘗試找出正確的長晶，摻雜條件，乃至製程處理條件，以獲得良好的元件特性。首先，針對材料中的n型p型摻雜，尤其是碲與鎂的摻雜，我們在碲摻雜的磷化鋁鎵銦中發現位於傳導帶下方0.165與0.385 eV兩個捕捉電子缺陷，這兩個缺陷與碲摻雜的本身有相當密切的關係，可發現隨著碲摻雜的增加，缺陷數目亦隨之增加，且兩者的缺陷數目與材料中的含鋁比例亦有相關連，在鋁鎵比例各為一半時，兩著之缺陷數目均達到最高值，另外，在鎂摻雜的材料中，並未發現任何缺陷。利用改變長晶過程中五族三族流量比例的實驗中，可發現一與磷空缺相關的缺陷，位於傳導帶下方0.65 eV，同樣在熱退火的實驗中，也發現應與磷空缺的缺陷，活化能為0.57 eV，兩者可能分別形成不同的磷空缺缺陷，或是與其他物質結合成複合缺陷型態，因此導致所形成的缺陷位子不同。最後再針對加碼射線的影響裝，我們發現加碼射線的照射可產生數個缺陷在磷化鎵銦材料中，分別為三個電子捕捉缺陷，其中一個為材料缺陷，位於傳導帶下方0.13 eV，另兩個為界面缺陷。同時，另發現有兩個電洞捕捉缺陷，一個為材料缺陷，位於價帶上方0.29eV處，另一個則為界面缺陷。

(AlxGa1-x)0.5In0.5P quaternary alloys, lattice matched to GaAs substrates, have been widely employed in space solar cells, visible wavelength laser diodes (LDs) and high-efficiency light-emitting diodes (LEDs). As the Al composition increases from 0 to 0.5, the direct bandgap (Γ) energy of the (AlxGa1-x)0.5In0.5P layer increases from 1.9eV to 2.26eV, which covers the red to yellow-green portion of visible spectrum. As generally known, deep levels in opto-electronic devices significantly reduce the efficiency. Therefore, investigation on the deep levels in AlGaInP materials is important. First, two majority carrier traps, N1 and N2, were observed in Te-doped AlGaInP alloys with activation energies of 0.165 and 0.385 eV, respectively. Both the trap concentrations were observed to be increased with elevating the Te concentration, indicating these traps as dopant-related defects. Furthermore, both dopant-related defects showed strong correlation with Al composition in AlGaInP alloys, both of which reached the maximum concentrations at around x=0.5. On the other hand, the deep levels in p-type AlGaInP alloys have also been studied, but there was no defects observed in Mg-doped AlGaInP by deep level transient spectroscopy measurement. Various V/III mole ratios were used for growing DLTS samples and a phosphorous vacancy related trap, P2, was found in the Te-doped AlInP when the V/III mole ratio is below 120. Meanwhile, the P2 concentration obviously increased with decreasing V/III mole ratio. This defect was an electron trap, with the activation energy of 0.65. Thermal-induced defects in AlInP have also been studied by annealing the samples at 400, 500, 600 and 700 ℃ for 30 mins under N2 ambient. The sample structure herein was Schottky diode due to its simple for analyzing the defects. A thermal-treatment-induced deep level, T2, was found in the AlInP layers when the annealing temperature was higher than 500℃. Meanwhile, the T2 concentration obviously increased with elevating the annealing temperature. The emission activation energy, Ea, of trap T2 deduced from the slope of the Arrhenius plot was around 0.57 eV. Both deep electron traps and hole traps created by gamma-ray irradiation in GaInP layers have been extensively studied. Three deep electron traps, GN1 GN2 and GN3, were observed, and verified as a bulk defect and two interface states, while GP1 and GP2, were identified as deep hole traps and verified as a bulk defect and a interface state. The activation energies deduced by Arrhenius plots of bulk traps GN1 and GP1 were around 0.13 and 0.29 eV.