MOCVD epitaxy of InAlN on different templates

InAlN epilayers were grown on high quality GaN and A1N templates with the same growth parameters. Measurement results showed that two samples had the same In content of～16%,while the crystal quality and surface topography of the InAlN epilayer grown on the AlN template,with 282.3"（002） full width at half maximum （FWHM） of rocking curve,313.5"（102） FWHM,surface roughness of 0.39 nm and V-pit density of 2.8×10⁸ cm^-2,were better than that of the InAlN epilayer grown on the GaN template,309.3",339.1",0.593 nm and 4.2×10⁸ cm^-2.A primary conclusion was proposed that both the crystal quality and the surface topography of the InAlN epilayer grown on the AlN template were better than that of the InAlN epilayer grown on the GaN template. Therefore,the AlN template was a better choice than the GaN template for getting high quality InAlN epilayers.     

Effect of a high temperature AlN buffer layer grown by initially alternating supply of ammonia on AIGaN/GaN heterostuctures

The effect of a high temperature AlN buffer layer grown by the initially alternating supply of ammonia （IASA） method on AlGaN/GaN heterostructures was studied. The use of AlN by the IASA method can effectively increase the crystalline quality and surface morphology of GaN. The mobility and concentration of 2DEG of AlGaN/GaN heterostuctures was also ameliorated.     

AlN单晶的位错腐蚀和红外吸收分析

The defects and the lattice perfection of an AlN（0001） single crystal grown by the physical vapor trans-port（PVT） method were investigated by wet etching, X-ray diffraction（XRD）, and infrared absorption, respectively.A regular hexagonal etch pit density（EPD） of about 4000 cm-2 is observed on the（0001） Al surface of an AlN single crystal.The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process.The XRD full width at half maximum（FWHM） of the single crystal is 35 arcsec, suggesting a good lattice perfection.Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm-1, respectively.These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.     

Effects of growth temperature on high-quality In0.2Ga0.8N layers by plasma-assisted molecular beam epitaxy

High-quality In_0.2Ga_0.8N epilayers were grown on a GaN template at temperatures of 520 and 580℃ via plasma-assisted molecular beam epitaxy. The X-ray rocking curve full widths at half maximum (FWHM) of (10.2) reflections is 936 arcsec for the 50-nm-thick InGaN layers at the lower temperature. When the growth temperature increases to 580℃, the FWHM of (00.2) reflections for these samples is very narrow and keeps similar, while significant improvement of (10.2) reflections with an FWHM value of 612 arcsec has been observed. This improved quality in InGaN layers grown at 580℃ is also reflected by the much larger size of the crystalline column from the AFM results, stronger emission intensity as well as a decreased FWHM of room temperature PL from 136 to 93.9 meV.     

Effects of growth temperature on high-quality In_(0.2)Ga_(0.8)N layers by plasma-assisted molecular beam epitaxy

正High-quality In_(0.2)Ga_(0.8)N epilayers were grown on a GaN template at temperatures of 520 and 580℃via plasma-assisted molecular beam epitaxy.The X-ray rocking curve full widths at half maximum(FWHM) of(10.2) reflections is 936 arcsec for the 50-nm-thick InGaN layers at the lower temperature.When the growth temperature increases to 580℃,the FWHM of(00.2) reflections for these samples is very narrow and keeps similar,while significant improvement of(10.2) reflections with an FWHM value of 612 arcsec has been observed.This improved quality in InGaN layers grown at 580℃is also reflected by the much larger size of the crystalline column from the AFM results,stronger emission intensity as well as a decreased FWHM of room temperature PL from 136 to 93.9 meV.     

Heteroepitaxial growth of thick α-Ga_2O_3 film on sapphire(0001)by MIST-CVD technique

The 8 μm thick single-crystalline α-Ga2O3 epilayers have been heteroepitaxially grown on sapphire(0001) substrates via mist chemical vapor deposition technique. High resolution X-ray diffraction measurements show that the full-widths-at-halfmaximum(FWHM) of rocking curves for the(0006) and(10-14) planes are 0.024° and 0.24°, and the corresponding densities of screw and edge dislocations are 2.24 × 106 and 1.63 × 109 cm-2, respectively, indicative of high single crystallinity. The out-ofplane and in-plane epitaxial relationships are [0001] α-Ga2O3//[0001] α-Al2O3 and [11-20] α-Ga2O3//[11-20] α-Al2O3, respectively.The lateral domain size is in micron scale and the indirect bandgap is determined as 5.03 eV by transmittance spectra. Raman measurement indicates that the lattice-mismatch induced compressive residual strain cannot be ruled out despite the large thickness of the α-Ga2O3 epilayer. The achieved high quality α-Ga2O3 may provide an alternative material platform for developing high performance power devices and solar-blind photodetectors.     

Growth of thick CdTe epilayers on GaAs substrates and evaluation of CdTe/n<Superscript>+</Superscript>-GaAs heterojunction diodes for an X-ray imaging detector

The growth characteristics of thick (100) CdTe epitaxial layers of a thickness up to 200 μm on a (100) GaAs substrate in a metal-organic vapor-phase epitaxy (MOVPE) system and fabrication of CdTe/n⁺-GaAs heterojunction diodes for their possible applications in low-energy x-ray imaging detectors are reported. The grown epilayers were of high structural quality as revealed from the x-ray double-crystal rocking curve (DCRC) analysis, where the full-width at half-maximum (FWHM) values of the (400) diffraction peaks was between 50 arcsec and 70 arcsec. The 4.2-K photoluminescence (PL) showed high-intensity bound-excitonic emission and very small defect-related peaks. The heterojunction diode fabricated had a good rectification property with a low value of reverse-bias current. The x-ray detection capability of the diode was examined by the time-of-flight (TOF) measurement, where good bias-dependent photoresponse was observed, but no carrier transport property could be deduced. It was found that the CdTe layer has a large number of trapping states as attributed to the cadmium-related vacancy and Ga-impurity, diffused from the substrate, related defect complexes.     

Research on the hydrogen terminated single crystal diamond MOSFET with MoO3 dielectric and gold gate metal

The single crystal diamond with maximum width about 10 mm has been grown by using microwave plasma chemical vapor deposition equipment.The quality of the grown diamond was characterized using an X-ray diffractometer.The FWHM of the (004) rocking curve is 37.91 arcsec,which is comparable to the result of the electronic grade single crystal diamond commercially obtained from Element Six Ltd.The hydrogen terminated diamond field effect transistors with Au/MoO3 gates were fabricated based on our CVD diamond and the characteristics of the device were compared with the prototype Al/MoO3 gate.The device with the Au/MoO3 gate shows lower on-resistance and higher gate leakage current.The detailed analysis indicates the presence of aluminum oxide at the Al/MoO3 interface,which has been directly demonstrated by characterizing the interface between Al and MoO3 by X-ray photoelectron spectroscopy.In addition,there should be a surface transfer doping effect of the MoO3 layer on H-diamond even with the atmospheric-adsorbate induced 2DHG preserved after MoO3 deposition.     

Investigation on the InAS1-xSbx epilayers growth on GaAs (001) substrate by molecular beam epitaxy

Undoped and Be-doped InAs1-xSbx (0 ≤ x ≤ 0.71) epitaxial layers were successfully grown on lattice mismatched semi-insulating GaAs (001) substrate with 2° offcut towards 〈 110〉.The effect of the InAs buffer layer on the quality of the grown layers was investigated.Moreover,the influence of Sb/In flux ratio on the Sb fraction was examined.Furthermore,we have studied the defects distribution along the depth of the InAsSb epilayers.In addition,the p-type doping of the grown layers was explored.The InAsSb layers were assessed by X-ray diffraction,Nomarski microscopy,high resolution optical microscopy and Hall effect measurement.The InAs buffer layer was found to be beneficial for the growth of high quality InAsSb layers.The X-ray analysis revealed a full width at half maximum (FWHM) of 571 arcsec for InAs0.87Sb0.13.It is worth noting here that the Hall concentration (mobility) as low (high) as 5 × 1016 cm-3 (25000 cm2V-1s-1) at room temperature,has been acquired.     

图形衬底上MOCVD生长光学性质改进的GaN

An improved GaN film with low dislocation density was grown on a C-face patterned sapphire substrate （PSS） by metalorganic chemical vapor deposition （MOCVD）. The vapor phase epitaxy starts from the regions with no etched pits and then spreads laterally to form a continuous GaN film. The properties of the GaN film have been investigated by double crystal X-ray diffraction （DCXRD）, atomic force microscopy （AFM） and photoluminescence （PL）, respectively. The full-width at half-maximum （FWHM） of the X-ray diffraction curves （XRCs） for the GaN film grown on PSS in the （0002） plane and the （1012） plane are as low as 312.80 arcsec and 298.08 acrsec, respectively. The root mean square （RMS） of the GaN film grown on PSS is 0.233 nm and the intensity of the PL peak is comparatively strong.     

High quality AlGaN grown on a high temperature A1N template by MOCVD

A high temperature A1N template was grown on sapphire substrate by metalorganic chemical vapor deposition. AFM results showed that the root mean square of the surface roughness was just 0.11 nm. Optical transmission spectrum and high resolution X-ray diffraction (XRD) characterization both proved the high quality of the A1N template. The XRD (002) rocking curve full width at half maximum (FWHM) was about 53.7 arcsec and (102) FWHM was about 625 arcsec. The densities of screw threading dislocations (TDs) and edge TDs were estimated to be～6×10~6 cm~(-2) and ～4.7×10~9 cm~(-2). A1GaN of A1 composition 80.2% was further grown on the A1N template. The RMS of the surface roughness was about 0.51 nm. XRD reciprocal space mapping was carried out to accurately determine the Al composition and relaxation status in the A1GaN epilayer. The XRD (002) rocking curve FWHM of the A1GaN epilayer was about 140 arcsec and (102) FWHM was about 537 arcsec. The density of screw TDs was estimated to be ～4×10~7 cm~(-2) and that of edge TDs was～3.3×10~9 cm~(-2). These values all prove the high quality of the A1N template and AlGaN epilayer.     

AlGaN基p-i-n型日盲紫外探测器材料的研制

采用金属有机气相外延(MOCVD)方法在(0001)面蓝宝石衬底上生长了AlN和高铝组分AlGaN材料。通过优化AlN和AlGaN材料的生长温度、生长压力和Ⅴ族元素/Ⅲ族元素物质的量比(nⅤ/Ⅲ)等工艺条件,得到了高质量的AlN和高铝组分AlGaN材料。AlN材料X射线双晶衍射ω(002)半宽为74 arcsec,透射光谱测试带边峰位于205 nm,带边陡峭;Al组分为45%的AlGaN材料X射线双晶衍射ω(002)半宽为223 arcsec,透射光谱测试带边峰位于272 nm,带边陡峭。采用此外延工艺方法生长了AlGaN基p-i-n型日盲紫外探测器材料并进行了器件工艺流片,研制出AlGaN基p-i-n型日盲紫外探测器,响应峰值波长为262 nm,在零偏压下的峰值响应度达到0.117 A/W。     

High-quality AlGaN layers over pulsed atomic-layer epitaxially grown AlN templates for deep ultraviolet light-emitting diodes

In this paper, we report the pulsed atomic-layer epitaxy (PALE) of ultrahigh-quality AlN epilayers over basal-plane sapphire substrates and their use as templates to grow high-quality AlGaN layers with Al content ranging from 0.3 to 1. Symmetric/asymmetric x-ray diffraction (XRD) and room-temperature (RT) photoluminescence (PL) measurements were used to establish the high-structural and optical quality. The XRD (002) and (114) rocking-curve full-width at half-maximum (FWHM) values of the PALE-grown AlN epilayers were less than 60 arcsec and 250 arcsec, respectively. Using these ultrahigh-quality layers as templates, Si-doped AlGaN layers with a large Al content from 30% to 100% were grown and used for milliwatt power sub-280-nm, deepultraviolet (UV) light-emitting diodes (LEDs).     

Optimization of High-Quality AlN Epitaxially Grown on (0001) Sapphire by Metal-Organic Vapor-Phase Epitaxy

A systematic study is performed to optimize aluminum nitride (AlN) epilayers grown on (0001) sapphire by metal-organic vapor-phase epitaxy. Specifically, the impact of the AlN nucleation conditions on the crystalline quality and surface morphology of AlN epilayers is studied. Atomic force microscopy (AFM) and x-ray diffraction (XRD) results reveal that the nucleation layer plays a critical role in the growth of subsequent layers. The magnitude of the TMAl flow of AlN nucleation layer is found to have a strong effect on the crystalline quality and surface morphology of the high-temperature (HT) AlN epilayer. A simple Al adatom-diffusion-enhancement model is presented to explain the strong dependence of the crystalline quality and surface morphology on TMAl flow. Furthermore, ammonia flow, nucleation temperature, and growth time of the AlN nucleation layer are found to affect the surface morphology and the crystalline quality as well. A trade-off is found between surface morphology and crystalline quality; that is, we do not obtain the best surface morphology and the highest crystalline quality for the same growth parameters. For optimized AlN nucleation layers and HT AlN epilayers, a clear and continuously linear step-flow pattern with saw-tooth shaped terrace edges is found by AFM on AlN epilayers. Triple-axis x-ray rocking curves show a full-width at half-maximum (FWHM) of 11.5 arcsec and 14.5 arcsec for the (002) and (004) reflection, respectively. KOH etching reveals an etch-pit density (EPD) of 2 × 10⁷ cm⁻², as deduced from AFM measurements.     

PVT法同质籽晶AlN晶体生长

为了获得高质量AlN晶体,通过物理气相传输(PVT)法,采用AlN籽晶进行AlN晶体生长,并通过双温区加热装置对衬底与原料之间的温差进行调节。研究结果表明,籽晶形核阶段,随着AlN籽晶与原料顶温差的减小,AlN的形核机制呈现三种模式,分别为岛生长模式、畴生长模式和螺旋位错生长模式;晶体生长阶段,通过增加AlN籽晶与原料顶温差来提高晶体生长速率,采用10℃/h的变温速率将温差从10℃增加为30℃时,AlN晶体生长模式不变,仍然保持螺旋位错生长模式,该生长模式下获得的AlN晶体结晶质量最高,(0002)面摇摆曲线半峰宽(FWHM)约为55 arcsec。     

InAlN薄膜MOCVD外延生长研究

为了研究不同压力和不同模板对InA lN薄膜外延生长的影响,分别选取以GaN为模板时生长压力为4.00、6.67和13.33 kPa,压力为4.00 kPa时模板为GaN和A lN这两组条件进行实验比较。研究发现,随着生长压力的增加,样品中In含量降低,样品的粗糙度则随压力的增加而增大;压力为4.00 kPa时,分别以摇摆曲线半高宽(FWHM)为86.97″的A lN和224.1″的GaN为模板,发现A lN模板上生长的InA lN样品(002)和(102)峰的FWHM值及表面粗糙度比上述GaN为模板生长的InA lN样品都要小很多。综合以上结果可初步得知:降低压力可以优化InA lN薄膜的表面形貌,增加In组分含量;采用高质量的A lN作模板能生长出晶体质量和表面形貌都比较好的InA lN薄膜。     

Al在生长InGaN材料中的表面活化效应

为了解决材料的界面平整度,改善材料的晶体质量,在Ⅲ-Ⅴ族氮化物(InGaN)材料的生长过程中,加入了Al掺杂剂.实验发现,InGaN材料的双晶衍射半宽从533arcsec(非掺Al)下降到399 arcsec(轻掺Al),PL光谱半宽变窄,从21.4 nm(非掺Al)降为20.9 nm(轻掺Al).研究结果表明,Al作为活性剂明显提高了InGaN材料质量,这将对改善LED和LD多量子阱材料和器件质量带来积极影响,目前还没有相关的文献报道.     

AlN外延薄膜的生长和特征

文章研究了AlN薄膜的晶体质量、表面形貌、应力等性质与AlN生长工艺的依赖关系。通过对低温成核厚度、成核温度和高温生长AlN所用Ⅴ／Ⅲ比的研究，制备出了具有较好晶体质量的AlN薄膜。高分辨三晶X射线衍射给出AlN薄膜的(002)和(105)的半高宽分别为16．9arcsec和615arcsec，接近国际上报道的较好结果。原子力显微镜对表面形貌的分析表明AlN薄膜的粗糙度为5．7nm。拉曼光谱表明E2(high)模向高能方向移动，说明蓝宝石上外延的AlN薄膜处于压应变状态。光学吸收谱在204nm处具有陡峭的带边吸收，也表明了AlN外延薄膜具有较好地晶体质量。