寬能隙銻化物與氮化物之磊晶成長、特性分析與元件研製

Abstract

在本論文中，我們使用有機金屬化學氣相磊晶法，成長寬能隙砷銻化鋁、氮化鎵、氮化銦鎵及其相關元件結構，並利用X光繞射、冷光激光、拉曼散射及霍爾效應等量測方法，來探討薄膜之光電物理特性。 實驗結果顯示，砷銻化鋁之固相組成與其薄膜成長溫度、反應源流量及比例有極大之關聯。高含銻量的薄膜僅能在V/III比例接近1之條件下製得。但是當V/III小於1、或銻反應源通入流量過高時，將導致固相鋁過剩、或固相銻析出等結果，進而破壞薄膜品質。而反應源TBAs於高溫下所產生的分解副反應，亦使得高溫成長薄膜之砷含量大幅下降。經由熱力學分析，我們推導出一嶄新之砷銻化鋁磊晶相圖，並獲得一較簡易之線性固、氣相磊晶相圖。藉由此相圖，我們能有效地控制薄膜組成，達成砷銻化鋁之全域磊晶。 此外，我們亦將砷銻化鋁應用於元件結構製備上，包括磷化銦蕭基元件及砷化銦鎵/砷銻化鋁單能障穿隧二極體等。研究結果顯示，利用砷銻化鋁可將傳統磷化銦之蕭基位障由0.45eV提升至0.76eV。在單能障穿隧結構中，亦能於室溫下獲得良好之負微分電阻特性，並於100K時得到一極高之峰谷電流比值4.2。此結果為目前所有類似結構中最優秀者。 在氮化鎵的研究方面，我們發現其薄膜特性不僅與低溫緩衝層之製備有關，其成長溫度亦有決定性之影響。最佳的緩衝層厚度、熱處理昇溫速率、及成長溫度分別為100~300埃、每分鐘75~100℃、及1,050~1,100℃。此外，我們也發現氮化鎵會由六角晶體結構，隨製備溫度之降低而演化為立方晶體結構，其相變點約在750℃。 在氮化銦鎵方面，研究結果顯示高溫製備之薄膜有較佳的結構與光學特性，但相對地不易獲致較高的固相銦組成。而過高的銦源流量、或過低的鎵源流量，都將不利於高固相銦組成薄膜之製備。當我們在熱力學分析中引入一高溫因子 ，我們可以有效地預測氮化銦鎵的固相組成與固相銦析出之條件。此外，我們也發現在磊晶成長時，氮化銦鎵薄膜中所能融入的最大銦含量，主要受限於高溫效應與銦原子之飽和蒸氣壓，這使得氮化銦鎵的磊晶成長區間，受到相當大的限制。

We have carried out systematic studies on the epitaxial growth of AlAs1-xSbx, GaN and InxGa1-xN compounds using metalorganic vapor phase epitaxy technique. Experimental data indicate that the solid composition of AlAsSb depends strongly on the input reactant flow rates and the growth temperature. A high Sb concentration of AlAsSb alloy can only be obtained at a V/III ratio close to 1, whereas too high the Sb flow rates and too low the V/III ratio will lead to the formation of Sb droplets and Al metal platelets, respectively. For AlAsSb prepared at high growth temperatures, the side reaction of TBAs, b-elimination, is believed to response for the result in a decrease of the As solid concentration. By employing a thermodynamic analysis, a novel phase diagram for AlAsSb with simpler solid-vapor distribution relationship was obtained, according to which the As solid concentration can be directly determined by the input As/Al mole flow rate ratio. The AlAs1-xSbx alloy was also used to fabricate two novel diodes, the enhanced InP Schottky diode and the In0.53Ga0.47As/AlAs0.44Sb0.56/In0.53Ga0.47As single barrier tunneling diode. By introducing AlAsSb into the conventional Schottky structure, the InP Schottky barrier height was improved greatly from 0.45eV to 0.76eV. For single-barrier tunneling diode, a negative differential resistance characteristic was successfully observed at 100 and 300K. A high peak-to-valley current ratio of 4.2 is obtained at 100K, which is the best value ever reported for such type of device. For GaN, the film quality appears to be very sensitive to the buffer layer property and the growth temperature. The optimized buffer layer thickness, temperature ramping rate and growth temperature are found to be around 100~300A, 75~100℃/min, and 1,000~1,050℃, respectively. A phase transition from hexagonal to cubic structure for GaN has been evidenced at a growth temperature around 750℃. The best quality of our GaN films in terms of FWHMs of x-ray and 300K-PL are as narrow as only 160 arcsec and 28meV, respectively. The corresponding electron mobility and carrier concentration also exhibit superior values of 330 cm^2/V and 1.1x10^17 cm^-3, respectively. Regarding to the InGaN growth, our experimental results indicate that the solid composition and characteristic of InGaN are determined not only by the growth temperature, but also by the TMGa and TMIn flow rates. The films with the good structural and optical properties can only be obtained at temperatures above 750℃. For the solid distribution, we found that too high the TMIn flow rate and too low the TMGa flow rate will both bring a decrease of In concentration solid, unfavorable to the high-In content InGaN growth. Besides, the thermodynamic analysis was also performed in our InGaN study. By introducing an empirical high-temperature factor in our modified InGaN growth model, we can successfully predict the solid-vapor distribution in InGaN and the appearance of In-droplets during growth. Based on thermodynamic arguments, the maximum allowed In solid concentration for a single phase InGaN is constrained primarily by the high temperature effect, such as In desorption, and the In saturation vapor pressure. By optimizing the growth conditions, we can obtain high quality InGaN epilayers with the narrow FWHMs of 150 arcsec and 92 meV for (0002) x-ray diffraction and 300K-PL peaks, respectively.