화학적 습식 에칭을 통한 AlN 와 GaN 단결정의 결함 및 표면 특성 분석

Abstract

화학적 습식 에칭을 통해 AlN와 GaN 단결정의 결함 및 표면 특성을 분석하였다. 화학적 습식 에칭은 단결정의 결함을 선택적으로 에칭하기 때문에 결정의 품질을 평가하는 좋은 방법으로 주목 받고 있다. AlN와 GaN의 단결정은 NaOH/KOH 용융액을 이용하여 에칭을 하였으며, 에칭 후 표면 특성을 알아보기 위해 주사전자현미경 (SEM)과 원자힘 현미경 (AFM)을 이용하였다. 에치 핏의 깊이를 측정하여 에칭 속도를 계산했다. 그 결과 AlN와 GaN 단결정 표면에는 두 개의 다른 형태에 에치 핏이 형성 되었다. (0001)면의 metal-face (Al, Ga)는 육각추를 뒤집어 놓은 형태를 갖는 반면 N-face (000)면은 육각형 형태의 소구 모양 (hillock structure)을 하고 있었다. 에칭 속도는 N-face가 metal-face (Al, Ga)보다 각각 약 109배 (Al)와 5배 (Ga)정도 빨랐다. 에칭이 진행되는 동안 에치 핏은 일정한 크기로 증가하다 서로 이웃한 에치 핏들과 합쳐지는 것으로 보여졌다. 또한 AlN와 GaN의 에칭 공정을 화학적 메커니즘을 통해 알아보았는데, 수산화 이온(OH-)과 질소의 dangling bond에 영향을 받아 metal-face (Al, Ga)와 N-face가 선택적으로 에칭 되는 것으로 추론된다.|The defects and surface polarity in AlN and GaN crystals were investigated by using wet chemical etching. The effectiveness and reliability of estimating the single crystals by defect selective etching in NaOH/KOH eutectic alloy have been successfully demonstrated. High-quality AlN and GaN single crystals were etched in molten NaOH/KOH eutectic alloy. The etching characteristics and surface morphologies were carried out by scanning electron microscope (SEM), atomic force microscope (AFM) and x-ray photoelectron spectroscopy (XPS). The etch rates of AlN and GaN surface were calculated by etching depth as a function of etching time. As a result, two-types of etch pits with different sizes were revealed on AlN and GaN surface, respectively. On etching rate calibration, it was found that N-face had approximately 109(Al) and 15(Ga) times higher etch rate than the metal-face of AlN and GaN, respectively. The size of etch pits increased with an increase of the etching time and they tend to merge together with a neighbouring etch pits. Also, the chemical mechanism of each etching process was discussed. It was found that hydroxide ion (OH-)and the dangling bond of nitrogen play an important role in the selective etching of the metal-face and N-face.; The defects and surface polarity in AlN and GaN crystals were investigated by using wet chemical etching. The effectiveness and reliability of estimating the single crystals by defect selective etching in NaOH/KOH eutectic alloy have been successfully demonstrated. High-quality AlN and GaN single crystals were etched in molten NaOH/KOH eutectic alloy. The etching characteristics and surface morphologies were carried out by scanning electron microscope (SEM), atomic force microscope (AFM) and x-ray photoelectron spectroscopy (XPS). The etch rates of AlN and GaN surface were calculated by etching depth as a function of etching time. As a result, two-types of etch pits with different sizes were revealed on AlN and GaN surface, respectively. On etching rate calibration, it was found that N-face had approximately 109(Al) and 15(Ga) times higher etch rate than the metal-face of AlN and GaN, respectively. The size of etch pits increased with an increase of the etching time and they tend to merge together with a neighbouring etch pits. Also, the chemical mechanism of each etching process was discussed. It was found that hydroxide ion (OH-)and the dangling bond of nitrogen play an important role in the selective etching of the metal-face and N-face.