Образование полуполярных III-нитридных слоев на поверхности Si(100), структурированной с помощью самоформирующейся наномаски

The growth of high-quality and crack-free GaN layers on a 5”φ Si (111) substrate has been carried out in metal-organic vapor phase epitaxy. A high-temperature-grown AlN/GaN multilayer buffer was inserted between a GaN layer and a Si substrate. To improve the crystalline quality of GaN and minimize the degree of wafer bending, the structural parameters of an AlN/GaN multilayer (e.g. number of pairs and thickness of each layer) were examined. From the results, two models of strain relaxation in the multilayer, namely, the introduction of a dislocation in the multilayer and the deformation of a strain field by a three-dimensional structure of AlN layers, are suggested. In addition, another role of the AlN/GaN multilayer structure, that of inducing compressive distortion in a subsequent GaN layer, was confirmed. On the AlN/GaN multilayer, a 1-µm-thick GaN layer was grown without crack formation. A dislocation density of 5 ×109 cm-2 determined by atomic force microscopy and a (002) X-ray rocking curve full width at half maximum of 700 arcsec were obtained in the 5”φ Si wafer region.

Growth of a GaN layer on a glass substrate by metal organic chemical vapor deposition

A major limitation in the growth of InGaN–GaN heterostructures is the requirement for cyclic ramping of the growth temperature of ∼200 °C. In conventional systems this temperature ramping is slow, and part of the InGaN layer may degrade before next GaN layer is deposited. We present here data from a novel growth system that overcomes this limitation and allows the growth of a higher quality GaN and InGaN layers than produced in our system by a conventional process. The system is based on Rapid Thermal MOCVD (RT-MOCVD) in which two sets of high power tungsten–halogen lamps were used to radiatively heat a low thermal mass susceptor with ramp rates up to ∼250 °C/s. This allows the fabrication of heterostructures by using temperature as a switch in starting or terminating a process step rather than applying the gas phase switching technique normally used in the standard MOCVD technique. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of single-domain GaN layers on Si(0 0 1) by metalorganic vapor-phase epitaxy

실리콘 기판 위에 GaN를 성장하기 위해서 AlN 완충층을 사용해 왔다. 그러나 AlN은 아직까지 high doping이 쉽지 않기 때문에, 이로 인해 AlN를 전자소자나 광소자 제작을 위한 완충층으로 이용하는 경우 직렬 저항의 증가라는 문제가 발생할 수 있다. 본 연구에서는 이러한 문제점을 개선하기 위해 AlN 완충층 대신에 금속 완충층을 사용하여 실리콘 기판 위에 GaN 박막 성장실험을 수행하였다. Al, Ti, Cr 그리고 Au 등을 금속 완충층으로 사용하여 실리콘 기판 위에 GaN 층을 성장하였다. 성장된 GaN 박막의 표면 특성을 분석하기 위해 광학현미경과 SEM을 사용하였고, 결정성과 광학적 특성을 평가하기 위하여 PL과 XRD 분석을 실시하였으며 AlN 완충층을 사용한 경우와 금속 완충층을 사용한 경우의 저항 차이를 확인하기 위하여 전류-전압 특성을 측정하였다. AlN buffer layers have been used for the growth of GaN layers on Si substrates. However, the doping of high concentration of carriers into AlN layers is still not easy, therefore it may cause the increase of series resistance when it is used for the electrical or optical devices. In this work, to improve such a problem, the growth of GaN layers on Si substrates were performed using metal buffer layers instead of AlN buffer layer. We tried combinations of Ti, Al, Cr and Au as metal buffer layers for the growth of GaN on Si substrates. Surface morphology was measured by optical microscope and scanning electron microscope (SEM), and optical properties and crystalline quality were measured by photoluminescence (PL) and X-ray diffractometer (XRD), respectively. Electrical resistances for both cases of AlN and metal buffer layer were compared by current-voltage (I-V) measurement.

One-, two- and three-flow metalorganic vapor phase epitaxy (MOVPE) methods have been compared in GaN growth, and each growth is analyzed by computational fluid dynamics (CFD). It is found that two-flow method shows better growth condition for achieving high quality layers compared to one- and three-flow methods. A GaN layer with high Hall mobility of 360 cm2/Vs is obtained by two-flow MOVPE growth despite no low-temperature buffer layer. The V/III decomposition ratio of NH2/GaCH3 is calculated by CFD simulation in gas phase just on substrate surface. The V/III ratio is in a narrow region to get high-mobility samples.

This paper reports on the growth of Cr‐doped GaN layers by metal organic vapor phase epitaxy (MOVPE) and their characterization for possible spintronic applications. We have used bis (cyclopentadienyl)chromium (Cp2Cr) to intentionally incorporate chromium (Cr) during GaN layer growth. The effects of the carrier gas, hardware setup, and growth temperature on the growth of Cr‐doped GaN were investigated. A linear dependence between mole fraction of Cp2Cr in the gas phase and incorporated Cr in the solid phase was found. The surface morphology was mostly influenced by carrier gas and growth temperature. A remanent magnetization was observed even above room temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The authors have studied the growth of bulk, freestanding zinc-blende (cubic) GaN layers by plasma-assisted molecular beam epitaxy (PA-MBE). They have established that the best structural properties of freestanding zinc-blende GaN can be achieved with initiation under Ga-rich conditions but without Ga droplet formation. It is difficult to initiate the growth of zinc-blende GaN, but it is even more difficult to sustain the growth of the pure zinc-blende polytype in thick layers without any wurtzite inclusions. In order to grow high quality freestanding cubic GaN layers, it is necessary to maintain the same growth conditions for about 1week. The best quality zinc-blende phase GaN was achieved in the first 10μm of the GaN layers. The authors have produced zinc-blende GaN substrates from our thick bulk GaN layers and they used the side previously attached to the GaAs substrate as the episide of these zinc-blende GaN substrates. They have demonstrated the scalability of the process by growing zinc-blende GaN layers on 2 and 3in. diameter wafers. The growth of freestanding bulk GaN layers has allowed them to refine the value for the lattice parameter of zinc-blende GaN as 4.510±0.005Å. They have demonstrated that the PA-MBE process developed has allowed them to grow freestanding AlxGa1−xN wafers.

Plasma-assisted electroepitaxy as a method for the growth of GaN layers

Growth of high quality GaN layers with AlN buffer on Si(1 1 1) substrates

Cubic GaN layers has been grown on (311)A GaAs substrates by MOVPE at relatively high growth temperature at 900 °C. Cubic GaN (311) grew on the (311)A GaAs with and in‐plane epitaxial relationship of [01‐1]GaN//[01‐1]GaAs and [200]GaN//[200]GaAs. Full width at half maximum of the cubic GaN (002) X‐ray rocking curve is less than 20 arc min, which is comparable to that of the cubic GaN grown on (001) substrate. The lattice constant is in the range of 4.502 to 4.506 Å. Even at the growth temperature as high as 900 °C, the interface between cubic GaN layer and GaAs substrate is remarkably smooth without any voids, owing to the suppression of the (111) surface steps on the (311)A substrate surface. These results indicate that the (311)A‐oriented GaAs is a candidate substrate for the MOVPE growth of cubic GaN layer in avoiding the thermal decomposition of GaAs and in improving the interface and surface morphologies. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper reports on the growth of high-quality GaN layers on Si C substrates by hot- wall MOCVD. Use of AlN buffer with a thickness exceeding 50 nm is employed for the GaN deposition and it is found to encompass most of the misfit defects. A n arrower X-ray rocking curve over asymmetric than over symmetric reflection is measured - full width at a half maximum (FWHM) of 350 arcsec vs. FWHM of 490 arcsec for 10.4 and 00.2 peaks, respectively, indicating high overall quality of the film. The free exciton photoluminescence emission peak has rather narrow FWHM of 5 meV. The typical thickness of the GaN layers is about 2 mm and they are completely depleted according to the capacitance-voltage profili ng, which corresponds to estimated residual doping of less than 5x10 14 cm -3 . Only in some cases when the GaN layer is not depleted, deep level transient spectroscopy is performed and two deep traps with activation energies of 0.26 and 0.59 eV below the conduction band are measured.

The studies of the growth kinetics of GaN layers grown on nitridated Si(111) substrates by plasmaassisted molecular beam epitaxy are presented. The nucleation and overgrowth of the separate GaN/Si(111) nanocolumns during single growth run is demonstrated. The technique of the in situ control of the GaN/Si(111) nanocolumns lateral size is proposed.

A high-quality crack-free AlN cap layer on GaN layer has been achieved using an AlN buffer layer directly grown on a silicon substrate at high temperature by radio frequency (RF) plasma-assisted molecular beam epitaxy. A two dimensional (2D) growth process guide to AlN cap layer of high grade crystal quality. The nucleation and the growth dynamics have been studied by in situ reflection high energy electron diffraction (RHEED) and ex situ by high resolution transmission electron microscopy (HR-TEM). The microstructure was investigated by energy-dispersive X-ray spectroscopy (EDX). It was disclosed that AlN is single crystalline with low defect. High densities of V-shaped pits were not detected at the interface between AlN and GaN layers. Contradictory the earlier reported V-shaped defects in nitride-based alloys; these V-shaped pits were condensed on top of the AlN layer because of H2 etching of the surface when a high temperature growth discontinuity between AlN and GaN layers.

Effect of the transition porous silicon layer on the properties of hybrid GaN/SiC/por-Si/Si(1 1 1) heterostructures