應用濺鍍氮化鋁緩衝層於氮化鎵發光二極體之研究

Abstract

本論文主要為應用濺鍍氮化鋁緩衝層在氮化鎵發光二極體之研究，首先探討氮化鎵薄膜成長於不同厚度之濺鍍氮化鋁緩衝層的成長模式及表面形貌，以成長氮化鎵薄膜之成長時間與表面反射率關係圖為基礎，利用掃描式電子顯微鏡量測不同時間點時的表面形貌並進行分析，接著使用X-ray繞射儀及單位面積缺陷數量測氮化鎵薄膜的品質，最後以金屬有機化學氣相磊晶機台成長之氮化鎵緩衝層一同成長氮化鎵發光二極體後，進行光電特性及光輸出功率的量測及比較。 由掃描式電子顯微鏡量測氮化鎵薄膜成長於不同厚度濺鍍氮化鋁緩衝層可知，隨著濺鍍氮化鋁厚度的減少，其氮化鎵薄膜成長時3D轉2D的過渡時間會延長，能減少氮化鎵薄膜的缺陷密度，也因濺鍍氮化鋁緩衝層厚度的不同，造成其表面附著結晶核密度的差異性，進而影響氮化鎵薄膜的成長。 由氮化鎵(102)面的半高寬量測分析及單位面積缺陷數量測結果顯示，氮化鎵薄膜成長於濺鍍氮化鋁緩衝層上，其氮化鎵薄膜品質比起成長於傳統型藍寶石基板上之X-ray(102)面的半高寬可由558arcsec減少至387arcsec，而單位面積缺陷數則隨著濺鍍氮化鋁緩衝層的厚度減少而降低，結果顯示具有濺鍍氮化鋁緩衝層成長氮化鎵薄膜可提升其薄膜品質。 最後將金屬有機化學氣相磊晶機台成長之氮化鎵緩衝層一同成長氮化鎵發光二極體後，以電流電壓量測系統量測結果，具有氮化鋁緩衝層之發光二極體，在操作電流20mA注入下，濺鍍氮化鋁緩衝層和以MOCVD成長之氮化鎵緩衝層，對發光二極體元件之電性並無顯著影響，以電流電壓量測系統量測發光二極體元件之逆向偏壓下的電流電壓曲線得以證明減少緩衝層的厚度能夠提升氮化鎵薄膜的品質，進而改善漏電流值。在光輸出功率曲線方面，20mA注入下，由3.40mW增加至4.53mW，光輸出功率提升了33%，顯示具有氮化鋁薄膜緩衝層可以有效減少氮化鎵薄膜與藍寶石基板間的晶格常數不匹配所產生的單位面積缺陷，因而改善氮化鎵薄膜的品質，提升內部量子效率及光輸出功率。

The purpose of this study was to investigate the application of sputtered AlN nucleation layers in GaN-based light-emitting diodes (LEDs). We first investigated the growth mechanism and surface morphology of GaN film growth on varying thicknesses of sputtered AlN nucleation layers. Based on GaN film growth time and surface reflectivity diagrams, we used SEM to measure the surface morphology at various times, conducted analysis, and then measured GaN film quality with X-ray diffraction and AFM image of etching pits density. Finally, after employing MOCVD to grow GaN nucleation layers with GaN-based light-emitting diodes, we measured and compared the optical properties and light output power. According to SEM-measured GaN film growth on sputtered AlN nucleation layers of varying thicknesses, as the sputtered AlN thickness decreases, the 3D to 2D growth recovery time of GaN films increases and the GaN film pit density decreases. Differences in the sputtered AlN nucleation layer thicknesses also produce differences in the surface crystal nucleation densities, further affecting GaN film growth. GaN (102) full width at half maximum (FWHM) measurement analysis and etching pit density measurement results show that the X-ray (102) FWHM of GaN films grown on sputtered AlN nucleation can be reduced from 558 arcsec to 387 arcsec compared to those grown on conventional sapphire, and the etching pit density declines as the sputtered AlN nucleation layer thickness decreases. The results show that GaN films grows on sputtered AlN nucleation layers can increase the film quality. Finally, after using MOCVD to grow GaN nucleation layers with GaN-based LEDs, the current-voltage measurement system results indicate that, with an injected current of 20 mA, sputtered AlN nucleation layers and MOCVD-grown AlN nucleation layers show no significant effect on the electrical properties of LEDs. The current-voltage curves adopted by the current-voltage measurement system under reverse bias verify that reducing the nucleation layer thickness can increase GaN film quality and further improve leakage current values. With an injected current of 20 mA, increasing from 3.40 mW to 4.53 mW, the light output power was increased by 33%. This demonstrates that AlN film nucleation layers can effectively reduce the etching pit density caused by incompatible GaN films and sapphire lattice constants, improving GaN film quality and increasing internal quantum efficiency and light output power.