光調制反射光譜技術分析氮化鎵表面費米能階及深層能皆之研究

Abstract

本論文利用光反射調制光譜技術（photoreflectance，PR）研究III-V 族氮化物的光電性質。除了對undoped-GaN、GaN LED、In0.4Ga0.6N樣品作基本的PR譜線分析之外，還進一步對undoped-GaN樣品進行表面費米能階釘住效應及DLTS兩方面的分析，在表面費米能階分析中，我們主要強調光電壓效應的不可忽略性，在深層能階的分析方面，則強調PR訊號強度與調制頻率的關係，並非完全與樣品深層能階有關，也有可能與表面能態為復和中心的機制有關，我們預測在低電場調制下，PR訊號強度與調制頻率的關係，由深層能階主控，在中、高電場調制下，則與表面能態為復和中心的機制有關。

In this work , photoreflectance (PR) was used to investigate optoelectronic properties of III-V nitride compounds.Not only identified PR features of undoped-GaN、 LED-structured GaN and In0.4Ga0.6N , we also surveyed surface Fermi level and deep levels of undoped-GaN . We found that the photovoltage is not negligible in studying surface Fermi level . Not as expected for the PR signal amplitude changing with modulation frequency by the charge released from deep levels , we found that the relation of PR lineshape to the modulation frequency for GaN is determined by the surface states instead of deep levels . We conclude that PR signal amplitude versus modulation frequency is dominated by deep levels in low field modulation and by surface states in intermediate and high field modulations.