Two kinds of heteroepitaxial systems, $In_xGa_{1-x}As(x<0.03)$/GaAs (one example of pseudo-heteroepitaxies) and GaAs/Si (one example of true heteroepitaxies) have been grown and characterized.
$In_xGa_{1-x}As$ epilayers on GaAs substrate, in the range of 00.003.
In order to grow high quality GaAs layers on Si substrates by metal organic chemical vapor deposition(MOCVD), surface morphology and crystallinity versus various growth conditions such as Si substrate orientation, high temperature bake-out, growth temperature and time for the nucleation step, and flow rate of $AsH_3$ and trimethylgallium(TMG), were investigated.
Using (100)Si 3˚ off-oriented toward [011], GaAs layers with a mirror surface can be grown easily, in comparison with exact (100)Si substrates. High temperature bake-out (900-950℃) and a nucleation step at low temperature are essential for the successful growth of GaAs-on-Si, and the good surface quality can be obtained with bake-out at 950℃ for 20 min and the nucleation step at 450℃ for 2.5 min with an As:Ga ratio of 50.
The surface becomes smoother as the thickness of GaAs layers on Si increases, but thin cracks appear for the 5.5 ㎛ thick GaAs layers. The molten KOH etching results show that no domains are revealed in the GaAs films and the etch pit density of these layers is $(1-2)×10^4$/㎠.
Cross-sectional transmission electron microscope(TEM) observations show that the misfit dislocations, which are generated at the interface, are confined in the narrow region (<5000Å) near the interface of GaAs/Si and some of them propagate into the GaAs surface. From the plan view TEM the dislocation density at the GaAs surface regin is measured about $10^8$/㎠.
The measured lattice parameters normal($a^1$) and parallel($a^{11}$) to the interface are 5.647 Å and 5.664-5.674 Å, respectively. While a does not depend on the layer thickness, a slightly depends on the layer thickness in the range 1-5.5 ㎛. On the other hand, the DCX rocking curve halfwidths decreased significantly with increasing the thickness of GaAs epilayer.
A DCX diffraction analysis of GaAs grown by MOCVD on misoriented Si substrates has demonstrated the existence of a tilt between the epilayer and the substrate. The magnitude of the relative tilt between the GaAs and Si [100] directions was about 0.05˚ and slightly varied according to the thickness of the GaAs epilayer.
이종접합(heteroepitaxy) 구조를 가지는 $In_xGa_{1-x}As$ (x<0.03)/ GaAs 및 GaAs-on-Si 을 화학증착법에 의해 성장시키고 특성들을 측정 분석하였다.
In/Ga alloy source를 사용하여 HCl-Ga-In-$AsH_3$-$H_2$ 계를 가지는 기상 epitaxy 법에 의해 $In_xGa_{1-x}As$ 에피결정을 성장시키기 위하여 열역학적 분석을 하였다. 에피결정 에서의 In 농도는 In/Gs alloy source 의 In 량에 의해 주로 결정되어지며 source 온도 및 증착 온도에는 크게 의존하지 않는다는 것을 계산결과로 부터 알 수 있었고, 이러한 계산결과를 적용하여 GaAs 기판위에 x 값이 0 과 0.03 사이의 $In_xGa_{1-x}As$ 에피결정을 성장하였다.
성장된 $In_xGa_{1-x}As$ 에피층의 조성비 x 값과 x 값의 변화에 따르는 전위밀도, 에너지갭, 깊은준위 등의 변화를 각각 X-선 회절법, 저온 photoluminescence (PL) 측정 및 접합과도용량 분광법 (DLTS) 등으로 조사하였다. 그결과 $In_xGa_{1-x}As$ 에피층의 조성비 x<0.02 범위에서의 밴드갭의 변화(ΔEg)는 ΔEg(eV)=1.68x 인 관계식으로 나타낼 수 있었으며, 또한 에피층 표면에서의 전위밀도는 x=0.003 근방에서 급격히 감소하였다. 한편 0 결정방향은 표면에 수직한 방향과 기판의 <001> 방향 사이에 위치하고 있고, 두 방향 사이의 각도 (misorientation)는 0.05˚로 측정되어졌다. 그리고 DCX회절에 의해 측정된 GaAs-on-Si의 반치폭은 300~450 arcsec 범위이며, GaAs 에피층의 두께가 두꺼워짐에 따라 줄어드는 경향을 보였다.
