Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

In this paper,we use the a-plane InGaN interlayer to improve the property of a-plane GaN.Based on the a-InGaN interlayer,a template exhibits that a regular,porous structure,which acts as a compliant effect,can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire.We find that the thickness of InGaN has a great influence on the growth of a-GaN.The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer.When the InGaN thickness exceeds a critical point,the a-GaN epilayer peels off in the process of cooling down to room temperature.This is an attractive way of lifting off a-GaN films from the sapphire substrate.     

Effects of V/III ratio on a-plane GaN epilayers with an InGaN interlayer

The effects of V/Ill growth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated. The surface morphology, crystalline quality, strain states, and density of basal stacking faults were found to depend heavily upon the V/III ratio. With decreasing V/III ratio, the surface morphology and crystal quality first improved and then deteriorated, and the density of the basal-plane stacking faults also first decreased and then increased. The optimal V/III ratio growth condition for the best surface morphology and crystalline quality and the smallest basal-plane stacking fault density of a-GaN films are found. We also found that the formation of basal-plane stacking faults is an effective way to release strain.     

Electron mobility limited by surface and interface roughness scattering in AlxGa1-xN/GaN quantum wells

The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.     

基于二维材料的III族氮化物外延

III族氮化物合金因其宽广的可调能隙和优良的光电性能,在照明、电力电子、通讯、能源等领域有巨大优势,促使其材料制备技术不断发展.如何解决III族氮化物异质外延过程中晶格及热胀失配对材料质量的影响,是当前的研究重点.近年来,二维材料作为一类新兴材料受到了极大的关注.借助二维材料层间弱键合的特性,有望降低III族氮化物的制备成本、提高晶体质量,并实现柔性器件的制备,从而将其应用领域拓宽至可穿戴器件、可折叠器件等.本文综述了近年来国内外在二维材料上制备III族氮化物的研究报道,介绍了石墨烯、六方氮化硼、过渡金属硫族化物等二维材料上制备氮化物的各种尝试和成果,总结了二维材料上III族氮化物制备的特点,并对其未来发展趋势做了展望.     

Growth and characterization of AlN epilayers using pulsed metal organic chemical vapor deposition

We report the growth of Al N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition(MOCVD). The sources of trimethylaluminium(TMAl) and ammonia were pulse introduced into the reactor to avoid the occurrence of the parasitic reaction. Through adjusting the duty cycle ratio of TMAl to ammonia from 0.8 to 3.0, the growth rate of Al N epilayers could be controlled in the range of 0.24 m/h to 0.93 m/h. The high-resolution x-ray diffraction(HRXRD) measurement showed that the full width at half maximum(FWHM) of the(0002) and(10-12) reflections for a sample would be 194 arcsec and 421 arcsec, respectively. The step-flow growth mode was observed in the sample with the atomic level flat surface steps, in which a root-mean-square(RMS) roughness was lower to 0.2 nm as tested by atomic force microscope(AFM). The growth process of Al N epilayers was discussed in terms of crystalline quality, surface morphology,and residual stress.     

Mobility limited by cluster scattering in ternary alloy quantum wires

The mobility limited by cluster scattering in ternary alloy semiconductor quantum wire(QWR) is theoretically investigated under Born approximation. We calculate the screened mobility due to clusters(high indium composition InGaN) scattering in the InxGa1 xN QWR structure. The characteristics of the cluster scattering mechanism are discussed in terms of the indium composition of clusters, the one-dimensional electron gas(1DEG) concentration, and the radius of QWR. We find that the density, breadth of cluster, and the correlation length have a strong effect on the electron mobility due to cluster scattering. Finally, a comparison of the cluster scattering is made with the alloy-disorder scattering. It is found that the cluster scattering acts as a significant scattering event to impact the resultant electron mobility in ternary alloy QWR.     

Effects of V/Ⅲ ratio on a-plane GaN epilayers with an InGaN interlayer

The effects of V/Ⅲgrowth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated.The surface morphology,crystalline quality,strain states,and density of basal stacking faults were found to depend heavily upon the V/Ⅲratio.With decreasing V/Ⅲratio,the surface morphology and crystal quality first improved and then deteriorated,and the density of the basal-plane stacking faults also first decreased and then increased.The optimal V/Ⅲratio growth condition for the best surface morphology and crystalline quality and the smallest basalplane stacking fault density of a-GaN films are found.We also found that the formation of basal-plane stacking faults is an effective way to release strain.     

Aluminum incorporation efficiencies in A- and C-plane AlGaN grown by MOVPE

The aluminum incorporation efficiencies in nonpolar A-plane and polar C-plane AlGaN films grown by metalorganic vapour phase epitaxy(MOVPE) are investigated. It is found that the aluminum content in A-plane AlGaN film is obviously higher than that in the C-plane sample when the growth temperature is above 1070?C. The high aluminum incorporation efficiency is beneficial to fabricating deep ultraviolet optoelectronic devices. Moreover, the influences of the gas inlet ratio,the Ⅴ/Ⅲ ratio, and the chamber pressure on the aluminum content are studied. The results are important for growing the AlGaN films, especially nonpolar AlGaN epilayers.