蓝宝石上AlN基板的MOCVD外延生长

结合 AlN 成核缓冲层技术和NH3流量调制缓冲层方法,采用 MOCVD 在(0001)面蓝宝石衬底上生长了 AlN 基板,用扫描电镜、原子力显微镜及 X 射线衍射仪对样品进行了表征,结果表明基板无裂纹,其平均粗糙度为0.35 nm,(0002)和(1012)回摆曲线 FWHM 分别为 37"和712".详细论述了AlN基板的生长模式、位错行为和应力释放途径.     

InAlN在不同模板上的MOCVD外延

在相同的生长条件下,分别在高质量的GaN 和 AlN 模板上生长InAlN外延层。 测试结果显示：本实验的两个样品的In组分均为～16%,但在AlN模板上生长的InAlN外延层的晶体质量和表面形貌都要优于在GaN模板上生长的样品。其中,在GaN模板上生长的InAlN样品的（002）和（102）峰摇摆曲线的半峰宽分别为309.3″和339.1″,样品表面的粗糙度为0.593 nm,v坑密度约为4.2108cm-2;而在AlN模板上生长的InAlN样品的（002）和（102）峰摇摆曲线的半峰宽分别为282.3″和313.5″,样品表面的粗糙度为0.39 nm,v坑密度约为2.8108cm-2 。综合以上结果可初步得知,在AlN模板上生长的InAlN外延层的晶体质量和表面形貌都要优于在GaN模板上生长的InAlN外延层,因此,相对于GaN模板来说,AlN模板更适宜高质量的InAlN 外延层的生长。     

应用厚缓冲层实现蓝宝石上高质量AlN外延层的MOCVD生长

在蓝宝石衬底上采用由低温AlN成核层、中温AlN生长层、温度渐变AlN生长层和高温AlN生长层组成的厚三维生长缓冲层来实现AlN外延层位错密度的减少和应力的释放.用光学显微镜、原子力显微镜(AFM)及X射线衍射仪对样品进行了表征,结果表明所生长外延层表面无裂纹,并显示出清晰的阶梯流表面形貌,其平均粗糙度为0.160 nm,KOH腐蚀坑密度为5.8×108 cm-2,(0002)和(10-12)回摆曲线FWHM分别为210”和396”.详细论述了AlN外延层的生长模式、位错行为和应力释放途径.     

AlGaN材料的MOCVD生长研究

文章研究了AlGaN材料的MOCVD生长机制。在位监控曲线表明,AlGaN材料生长过程是由三维生长逐渐过渡到二维生长,由于Al原子表面迁移率太小,随着TMAl流量的增加,需要更长的时间才能出现二维生长,材料质量也随着Al组分的增加而下降,AlGaN的表面形貌也变差。随着TMAl流量的增加,AlGaN材料的生长速率反而下降,这是由于Al原子阻止了Ga原子参与材料生长。实验还发现,由于TMAl与NH3 之间存在强烈的寄生反应,AlGaN材料中的Al组分远小于气相中的Al组分。文中简单探讨了提高AlGaN材料质量的生长方法。     

基于MOCVD高/低温调制生长AlN模板材料方法

宽禁带半导体紫外光电器件和功率半导体器件的发展对AlN材料和高Al组分AlGaN材料有着迫切的需求.由于缺乏大尺寸AlN同质衬底,基于异质外延生长的AlN模板材料成为了宽禁带半导体器件制造的最佳选择.但是,由于Al原子表面迁移能力较差,AlN外延材料表面易呈现岛状生长模式,导致AlN模板材料的晶体质量和表面质量较差,严...     

MOCVD生长高Al组分AlGaN材料研究

报道了用MOCVD在蓝宝石衬底上生长日盲型AlGaN基紫外探测器用的高质量AlN、AlGaN材料。通过优化AlN、AlGaN生长的工艺条件,如生长温度、生长压力及Ⅴ/Ⅲ比等,得到了器件级高质量的AlN、AlGaN外延材料。AlN外延膜X射线双晶衍射ω(002)面扫描曲线半高宽为97",ω(102)面扫描曲线半高宽为870",Al0.6Ga0.4N外延膜双晶衍射ω(002)面扫描曲线半高宽为240";使用原子力显微镜(AFM)对两种样品5μm×5μm区域的表面平整度进行了表征,AlN外延膜的粗糙度(Rms)为8.484nm,Al0.6Ga0.4N外延膜的粗糙度为1.104nm;透射光谱测试显示AlN和Al0.6Ga0.4N吸收带边分别为205nm和266nm,且都非常陡峭。     

蓝宝石衬底上AlGaN外延材料的低压MOCVD生长

采用低温AlN成核层在1180℃温度下在(0001)蓝宝石衬底上用低压MOCVD设备生长了AlGaN外延层.Al组分高达0.6、厚度大于1μm的AlGaN外延层表面光亮,晶体质量较好,(0002)X射线衍射回摆曲线半峰宽FWHM为853弧秒.当反应室气压从5×103Pa降到2×103Pa后, AlGaN 外延层的生长速率和固相Al组分都显著提高.     

HVPE法生长AlN薄膜材料

利用自制立式HVPE设备,在蓝宝石衬底上进行了不同载气情况下AlN的生长试验,生长温度1 000℃。在采用H2作载气情况下,由于预反应严重,没能生长出AlN薄膜,只得到一些白色AlN粉末;而在分别采用Ar和N2作载气的情况下,则成功生长出AlN薄膜,但由于生长温度低,AlN生长均为岛状生长模式。在生长速率较快时,AlN薄膜是以〈0001〉AlN为主的AlN多晶;而在较低生长速率下,得到的AlN薄膜由为〈0001〉取向的AlN岛组成。试验还发现:用Ar作载气更有利于AlN晶核的横向生长,用N2作载气则有相对高得多的AlN成核密度。     

MOCVD生长的全组分InGaN材料

利用金属有机物化学气相淀积(MOCVD)方法在C面蓝宝石衬底上制备了全组分InGaN薄膜,通过改变生长温度和In/Ga比例成功调控了InGaN合金组分和带隙宽度。利用不同的物理表征手段系统研究了InGaN薄膜的晶体结构和光电学性质,XRD和Hall等测试结果表明:富Ga的InGaN薄膜具有较好的晶体质量,背景电子浓度基本均比富In的InGaN低一个数量级。同时,结合光致发光谱和光学透射谱研究了InGaN合金带隙随In组分的变化关系。     

高温AlN为模板的AlGaN基p-i-n背照式日光盲探测器

第一次报道了以高温AlN为模板层的AlGaN基p-i-n背照式日光盲探测器的制作和器件特性.利用MOCVD方法在(0001)面的蓝宝石衬底上生长了探测器的AlxGa1-xN多层外延材料.在无需核化层的高温AlN模板上生长了p-i-n背照式日光盲探测器的无裂纹高Al组分(0.7)AlGaN多层外延结构.利用在线反射监测仪、三轴X射线衍射及原子力显微镜表征了外延材料的晶体质量.在1.8V的反向偏压下,制作的探测器表现出了日光盲响应特性,在270nm处最大响应度为0.0864A/W.具有约3.5V的正向开启电压,大于20V的反向击穿电压,在2V的反向偏压下暗电流小于20pA.     

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.     

Four-inch high quality crack-free AlN layer grown on a high-temperature annealed AlN template by MOCVD

In this work, based on physical vapor deposition and high-temperature annealing (HTA), the 4-inch crack-free high-quality AlN template is initialized. Benefiting from the crystal recrystallization during the HTA process, the FWHMs of X-ray rocking curves for (002) and (102) planes are encouragingly decreased to 62 and 282 arcsec, respectively. On such an AlN template, an ultra-thin AlN with a thickness of ~700 nm grown by MOCVD shows good quality, thus avoiding the epitaxial lateral overgrowth (ELOG) process in which 3–4 μm AlN is essential to obtain the flat surface and high crystalline quality. The 4-inch scaled wafer provides an avenue to match UVC-LED with the fabrication process of traditional GaN-based blue LED, therefore significantly improving yields and decreasing cost.     

Four-inch high quality crack-free AIN layer grown on a high-temperature annealed AIN template by MOCVD

In this work,based on physical vapor deposition and high-temperature annealing (HTA),the 4-inch crack-free high-quality AIN template is initialized.Benefiting from the crystal recrystallization during the HTA process,the FWHMs of X-ray rock-ing curves for (002) and (102) planes are encouragingly decreased to 62 and 282 arcsec,respectively.On such an AIN template,an ultra-thin AIN with a thickness of ～700 nm grown by MOCVD shows good quality,thus avoiding the epitaxial lateral over-growth (ELOG) process in which 3-4μm AIN is essential to obtain the flat surface and high crystalline quality.The 4-inch scaled wafer provides an avenue to match UVC-LED with the fabrication process of traditional GaN-based blue LED,therefore signific-antly improving yields and decreasing cost.     

6H-SiC衬底上采用不同厚度AlN缓冲层对GaN外延层的影响

采用不同厚度AlN作为缓冲层在6H-SiC衬底上生长了GaN外延层,并利用X射线衍射,拉曼散射和透射电子显微镜等对GaN性质进行了研究。AlN缓冲层的应变状态对GaN的晶体质量和表面形貌有很大影响。较厚的AlN缓冲层会导致GaN表面出现裂纹,而太薄的AlN缓冲层会导致GaN层较高的位错密度,从而恶化器件性能。分析了GaN产生裂纹和高位错密度的机制,并采用较优厚度（100nm）的AlN缓冲层生长出高质量的GaN外延层。     

Characteristics of GaN grown on 6H-SiC with different AlN buffers

Characteristics of GaN grown on 6H-SiC (0001) substrates using different thicknesses of AlN buffers are studied. It is found that the surface morphology and crystal quality of GaN film closely depends on the strain state of the AlN buffer. For a thicker AlN buffer, there are cracks on GaN surface, which make the GaN films unsuitable for applications. While for a thinner AlN buffer, more dislocations are produced in the GaN film, which deteriorates the performance of GaN. Possible generation mechanisms of cracks and more dislocations are investigated and a ～100 nm AlN buffer is suggested to be a better choice for high quality GaN on SiC.     

低欧姆接触MOCVD生长的AlN/GaN HEMT

AlN/GaN high-electron-mobility transistors(HEMTs)on SiC substrates were fabricated by metalorganic chemical vapor deposition(MOCVD)and then characterized.An Si/Ti/Al/Ni/Au stack was used to reduce ohmiccontactresistance(0.33 mm)atalowannealingtemperature.Thefabricateddevicesexhibitedamaximum drain current density of 1.07 A/mm(VGS D1 V)and a maximum peak extrinsic transconductance of 340 mS/mm.The off-state breakdown voltage of the device was 64 V with a gate–drain distance of 1.9 m.The current gain extrinsic cutoff frequency fT and the maximum oscillation frequency fmax were 36 and 80 GHz with a 0.25 m gate length,respectively.     

Investigations of GaN growth on the sapphire substrate by MOCVD method with different AlN buffer deposition temperatures

The effects of different AlN buffer deposition temperatures on the GaN material properties grown on sapphire substrate was investigated. At relatively higher AlN buffer growth temperature, the surface morphology of subsequent grown GaN layer was decorated with island-like structure and revealed the mixed-polarity characteristics. In addition, the density of screw TD and leakage current in the GaN film was also increased. The occurrence of mixed-polarity GaN material result could be from unintentional nitridation of the sapphire substrate by ammonia (NH₃) precursor at the beginning of the AlN buffer layer growth. By using two-step temperature growth process for the buffer layer, the unintentional nitridation could be effectively suppressed. The GaN film grown on this buffer layer exhibited a smooth surface, single polarity, high crystalline quality and high resistivity. AlGaN/GaN high electron-mobility transistor (HEMT) devices were also successfully fabricated by using the two-step AlN buffer layer.     

Study on Mg memory effect in npn type AlGaN/GaN HBT structures grown by MOCVD

AlGaN/GaN npn heterojunction bipolar transistor structures were grown by low-pressure MOCVD. Secondary ion mass spectroscopy (SIMS) measurements were carried out to study the Mg memory effect and redistribution in the emitter-base junction. The results indicated that there is a Mg-rich film formed in the ongrowing layer after the Cp₂Mg source is switched off. The Mg-rich film can be confined in the base section by switching off the Cp₂Mg source for appropriate time before the end of base growth. Low temperature growth of the undoped GaN spacer suppresses the Mg redistribution from Mg rich film. The delay rate of the Mg profile in sample C with spacer growing in low temperature is about 56 nm/decade, which becomes sharper than 80 nm/decade of the samples A and B without low temperature spacer.