초록 ▼

본 연구에서는 MBE법에 의한 고품위 GaAs 에피층 및 저온 GaAs 에피층 성장기술과 성장된 GaAs 에피층의 특성평가 기술을 개발하기 위하여 다음과 같은 내용의 연구를 수행하였다. 1. MBE를 이용하여 undoped 및 Si-doped GaAs layer를 (100) undoped 반절연 기판위에 성장하였고 이에 대한 전기적 및 광학적 특성을 조사하였다. Undoped GaAs층의 성장에서는 PL측정 결과로부터 As/Ga의 비가 20, 성장온도가 570℃일때 반폭치(FWHM)가 1.14meV인 결정성이 좋은 시료가 얻어졌으

본 연구에서는 MBE법에 의한 고품위 GaAs 에피층 및 저온 GaAs 에피층 성장기술과 성장된 GaAs 에피층의 특성평가 기술을 개발하기 위하여 다음과 같은 내용의 연구를 수행하였다. 1. MBE를 이용하여 undoped 및 Si-doped GaAs layer를 (100) undoped 반절연 기판위에 성장하였고 이에 대한 전기적 및 광학적 특성을 조사하였다. Undoped GaAs층의 성장에서는 PL측정 결과로부터 As/Ga의 비가 20, 성장온도가 570℃일때 반폭치(FWHM)가 1.14meV인 결정성이 좋은 시료가 얻어졌으며, carrier농도가 1.5×$10^{14} cm^{-3}$미만이고, Hall mobility가 300K에서 579㎠/V-s인 시료가 얻어졌다. Si-doped GaAs층의 성장에는 ODLTS, DLTS 및 CV 측정으로 부터 2개의 hole deep level을 관측하였고, 전자 ？이 거의 없으며, 1%정도의 균일한 불순물 농도를 가진 시료를 얻을 수 있었다. 2. 250℃의 기판온도에서 분자선 에피탁시에 의해 성장된 LT GaAs의 물성을 RHEED, double cyrstal x-ray (DCX), Raman spectroscopy, photoluminescence(PL)에 의해 관찰 하였다. 저온 GaAs란 400℃ 이하의 성장온도에서 성장된 epilayer를 말하며, 이 재료는 전기적으로 고저항이며, 광학적으로 낮은 감도를 나타내는 특성을 보인다. 이것은 성장중 As-rich 조건하에서 형성된 excess As precipitates, As-antisite defect등이 epilayer내에 고농도의 deep level을 형성하여 전도성 carrier들을 포획하는 것으로 알려져 있다. 3. Micro Raman을 이용하여 MBE 방법에 의해 성장된 GaAs 표면에서의 point defect들을 조사하였다. 본 연구에서 조사된 Point defect로는 α-, β-type oval defect, whisker defect, peacock defect가 있으며, 이중에 whisker defect가 가장 나쁜 결정성을 나타냈다. α-type oval defect는 성장층의 두께가 증가함에 따라 그 크기와 밀도가 증가했으나, TO/LO 비는 감소하였다. 그리고 β-type oval defect는 α-type oval defect보다 더 좋지않은 결정성을 나타냈다.

Abstract ▼

Ⅰ. Purpose and Significance of the Study The purpose of this research is to develope a growth technique of high-quality GaAs epilayers by molecular beam epitaxy(MBE) at low and/or high temperatures and characterization methods of the epilayers. In the fabrication of GaAs-based devices such as MESF

Ⅰ. Purpose and Significance of the Study The purpose of this research is to develope a growth technique of high-quality GaAs epilayers by molecular beam epitaxy(MBE) at low and/or high temperatures and characterization methods of the epilayers. In the fabrication of GaAs-based devices such as MESFETs, MMICs, etc., there are, as problems caused by using the semi-insulating GaAs substrate, backgating or sidegating effects, hysteresis in $I_{ds}-V_{ds}$ characteristics, light sensitivity, low source-drain breakdown voltage, low output-gain in RF wavelength, etc.. Of these, the backgating phenomenon has been recognized as the most deleterious problem in the application to digital/analog circuits. Therefore, a number of research groups have tried to solve the problem by making use of a buffer layer between the active layer and substrate of a device. And undoped GaAs, AlGaAs, superlattice structures, etc. have been proposed as the possible materials, but these are not enough to completely solve the problem. Of recent, F.W. Smith, et al. have proposed that the GaAs buffer layer grown by MBE at low temperature prevent the backgating effect in GaAs MESFET. Which has spurred other groups to investigate the electrical, optical, and crystallographical characteristics of low-temperature GaAs epilayers. Thus, our research, to realize a growth technique of high-quality GaAs epilayers by MBE at low and/or high temperatures and characterization methods of the epilayers, would result in the application into high-performance GaAs MESFETs and new GaAs semiconductor devices.Ⅱ. Results and Conclusions Undoped and Si-doped GaAs layers have been grown on (100) semi-insulating GaAs substrate by molecular beam epitaxy (MBE) and characterized by using not only a mass spectrometer and a reflection high-energy electron diffraction (RHEED), but also Hall measurements, photoluminescence (PL). In the undoped MBE growth, the p-type GaAs layers with the good surface morphology were grown under the growth conditions of the substrate temperatures ranging from 570 to 590℃ and the As/Ga ratio from 17 to 22. In the samples with the growth rates of the ranges of 0.9 ~ 1.1 μm/h, the impurity concentrations were in the ranges of 1.5 × $10^{14}{\sim}5.6 {\times} 10^{14} cm^{-3}$ with the Hall mobilities of 590 ~ 410 ㎠/V-sec. In the Si-doped GaAs, the n-type GaAs layers with low electron trap, two hole deep level and uniform doping profile(>1%) were measured by DLTS, ODLTS and CV. GaAs layers grown by molecular beam epitaxy (MBE) at substrate temperature ~250℃ were studied using reflection of high energy electron diffraction (RHEED), double crystal x-ray (DCX), raman spectroscopy, and photoluminescence(PL) techniques. For unannealed LT GaAs layers, RHEED pattern revealed enhancement of crystallinity under As-rich condition, and DCX diffraction revealed increase of 1.1% ~ 1.7% in the lattice parameter in comparision with bulk GaAs. On the other hand, For annealed layers, DCX diffraction showed lattice relaxation by rapid thermal annealing(RTA), and Raman spectroscopy showed that crystallinity was enhanced as RTA temperature increases. Point defects of GaAs surface layers grown by molecular beam epitaxy (MBE) have been investigated by using μ-Raman. Especially, oval defects and whisker defects, the most common macroscopic defects, in MBE GaAs were focused in this study. In Raman spectroscopy for the oval defect and the whisker defect, TO phonon mode of the 269 cm-1 peak in GaAs was observed. This indicates that both the oval defect and the whisker defect can include the armopholized surface. The TO/LO ratio is in the range from 0.2 to 0.4 for the oval defect and from 0.4 to 1.4 for the whisker defect, respectively. Therefore, the whisker defect shows the worst crystallinity in defects. In the sample grown under the condition that the substrate temperature is 580℃ with the As/Ga ratio of 20, the oval defect density is about 200 $cm^{-2}$ at the growth thickness of 5 μm. The density and the size of α-type oval defect are increased with the increased thickness of the epilayer, while the TO/LO ratio decreases. The whisker defect reduced drastically under an optimum growth condition. From this result, it is thought that the oval defect might be originated from the Ga-related complex from the Ga source and that the whisker defect from unstable growth condition.

목차 Contents

• 제 1 장 서 론...21
• 제 1 절 연구개발의 목적과 범위...21
• 제 2 절 보고서의 구성...23
• 제 2 장 MBE에 의한 고품위 GaAs 성장...25
• 제 1 절 MBE 성장...25
• 제 2 절 MBE GaAs의 특성분석...27
• 제 3 장 저온 MBE로 성장된 GaAs 에피층의 특성...39
• 제 1 절 시료준비 및 실험...39
• 제 2 절 저온 MBE GaAs의 특성분석...40
• 제 4 장 MBE GaAs의 표면결함에 대한 Micro 라만 분광학...51
• 제 1 절 Micro 라만장치 및 방법...51
• 제 2 절 MBE GaAs 에피층의 표면결함...53
• 제 5 장 종합적 결론 및 건의 사항...65
• 제 1 절 종합적 결론...65
• 제 2 절 건의사항...67
• 참 고 문 헌...68