超晶格插入层对Si基上GaN薄膜位错密度的影响

为了降低MOCVD外延生长Si基GaN的缺陷密度,尝试引入超品格插入层.界面突变的超晶格插入层能有效地阻挡由缓冲层延伸出来的位错.即使超晶格本身也产生位错,但位错的产生率比阻挡率低,所以超晶格总体起阻挡作用,可以减少后续生长的 HT-GaN(高温氮化镓)的位错密度.研究了超晶格厚度对 HT-GaN 的位错密度的影响.比较了超晶格厚度不同的3个样品,并采用高分辨双晶X射线衍射(DCXRD)对CaN进行结晶质量的分析,分别用 H3PO4 H2SO4 混合溶液和熔融 KOH 对样品进行腐蚀并用扫描电子显微镜(SEM)对腐蚀的样品进行观察.用 H3PO4 H2SO4 腐蚀过的样品比用KOH 腐蚀过的样品的位错密度大,进一步验证了之前有报道过的 H3PO4 H2SO4 溶液同时腐蚀螺位错和混合位错而 KOH只腐蚀螺位错.分析结果表明.引入适当厚度的超晶格插入层,可以有效地降低后续生长的 GaN 的位错密度.     

生长气体流量对SiC单晶缺陷的影响

实现了熔融KOH进行SiC体单晶择优腐蚀估测缺陷密度的方法.本文报道了采用该技术对体SiC单晶缺陷密度估测的结果.腐蚀会在Si面形成六边形腐蚀坑,在C面形成圆形腐蚀坑.腐蚀速率和蚀坑形状与SiC生长工艺有关.对在高生长气流量下用PVT工艺制备的SiC样品,其刃位错、螺位错与微管密度分别为2.82×105,94和38cm-2;对在低生长气流量下用PVT工艺制备的SiC样品,其上述缺陷密度分别为9.34×105,2和29cm-2.结果表明:随着生长气体流量的增加,由于避免了N2掺杂,刃位错密度下降.     

生长气体流量对SiC单晶缺陷的影响

实现了熔融KOH进行SiC体单晶择优腐蚀估测缺陷密度的方法.本文报道了采用该技术对体SiC单晶缺陷密度估测的结果.腐蚀会在Si面形成六边形腐蚀坑,在C面形成圆形腐蚀坑.腐蚀速率和蚀坑形状与SiC生长工艺有关.对在高生长气流量下用PVT工艺制备的SiC样品,其刃位错、螺位错与微管密度分别为2.82×105,94和38cm-2;对在低生长气流量下用PVT工艺制备的SiC样品,其上述缺陷密度分别为9.34×105,2和29cm-2.结果表明:随着生长气体流量的增加,由于避免了N2掺杂,刃位错密度下降.     

腐蚀坑处氮化镓二次MOCVD外延生长的特性

利用熔融KOH液对单层Ga N腐蚀后进行二次MOCVD外延生长,对不同二次生长时间的薄膜及生长前的薄膜进行扫描电子显微、X射线衍射和光致发光测试,实验结果表明二次生长2 h的薄膜具有最低的位错密度和最好的光学特性.在腐蚀坑处,坑中早期的慢速生长及后期的侧向生长都抑制穿透螺位错的生长,坑边缘与中心的非对称生长会引入新的穿透刃位错,莲花状坑结构相遇连通可以使连通处的穿透刃位错消失.     

In Ga As/Ga As超晶格的界面研究

In_xGa_(1-x)As/Ga As之间晶格失配度与X成线性关系,其最大值为7％。因而当外延层厚度大于临界厚度时在界面会产生微缺陷,这些缺陷对其材料性能有很大影响。因此对In x Ga_(1-x)As Ga As界面研究就显得很重要。本工作就GaAs衬底上MBE生长In_(0.2)Ga_(0.8)As/Ga As超晶格样品进行平面,断面的TEM研究。实验结果表明超晶格平整,均匀,只看到位错一种微缺陷。GaAs衬底内位错。表面机械损伤会在超晶格层内引入位错。在In Ga As Ga As界面上失配位错情况如图1所示。图1a为[110]方向衬象,可见界面上位错线及露头(箭头所示)倾转约30,在图1b中看到位错网络,箭头所示位错为1a中所示的露头。     

掺C高阻GaN的MOCVD外延生长

利用金属有机物化学气相沉积(MOCVD)技术在蓝宝石衬底上制备了Ga N∶C薄膜。为得到高阻(或半绝缘)的Ga N薄膜,研究了源(CCl4)流量和载气对MOCVD外延Ga N薄膜电学性能的影响,发现CCl4流量和载气对实现高阻的Ga N影响很大。当Ga N缓冲层采用N2作为载气,CCl4的流量为0.016μmol/min时成功实现了Ga N的高阻生长,样品A2的方块电阻高达2.8×107Ω/sq。经原子力显微镜(AFM)测试显示,样品的表面形貌较好,粗糙度均在0.3 nm附近,说明C掺杂对外延Ga N薄膜的表面形貌没有大的影响。低温荧光光谱测试显示黄光峰与刃型位错有关。     

与GaN晶格匹配的InAlN分子束外延生长及其性能北大核心CSCD

采用等离子体辅助的分子束外延(MBE)方法制备了InAlN外延薄膜,探讨了InAlN材料In原子数分数和生长条件的关系,以及等效束流强度(BEP)对材料质量的影响。绘制了InAlN关于温度与In和Al BEP的生长相图,经过优化后生长了与GaN晶格匹配的InAlN外延薄膜。使用高分辨率透射电子显微镜、X射线衍射仪、原子力显微镜和阴极荧光光谱(CL)对制备的InAlN材料进行了测试和表征。结果表明,InAlN/GaN异质界面清晰,In_(0.18)Al_(0.82)N外延材料(002)面X射线衍射峰半高宽为263 arcsec,表面粗糙度仅为0.23 nm,CL发光波长为283 nm,弯曲系数为5.2 e V,根据CL图像估算的材料位错密度约为2×108cm-2。     

Ⅲ/Ⅴ比对GaN等离子体辅助MBE生长的影响

在射频（RF）等离子体辅助分子束外延（MBE）系统中，采用低温缓冲层等一系列生长工艺制备出二维生长模式的GaN材料；通过研究Ⅲ／Ⅴ比的调节对GaN生长的影响，确定了微富Ga的MBE生长GaN的优化条件；对GaN富Ga和富N状态的表面形貌和结构进行了比较，富Ga条件下的GaN具有更好的表面和材料特性；通过Hall和光致发光（PL）谱测试研究了GaN的电学和光学性质，GaN的黄带发光（YL）与GaN中生成能最低的ⅤN和VGa缺陷态有关。     

调制掺杂AlxGa1-xN/GaN异质结中AlxGa1-xN势垒层表面态及其他局域态性质研究

通过测量调制掺杂Al0.22Ga0.78N/GaN异质结样品的变频电容-电压(C-V)特性,对Al0.22Ga0.78N势垒层表面态的性质进行了研究.结果发现在小偏压下,样品的电容随着测量信号频率的增加而下降,说明势垒层中存在表面态.实验数据分析表明:表面态密度约为1013cm-2量级,表面态的时间常数比势垒层中其他局域态大.随着空间隔离层厚度的增加,势垒层中其他局域态密度随之增加.在金属电极和Al0.22Ga0.78N势垒层之间加入Si3N4绝缘层可以对表面态起到显著的钝化作用,使表面态密度降为～1012cm-2量级.     

Q2D半导体电子和空穴统计

用半导体统计方法导出准二维半导体自由载流子面密度的数学表达式 ,并给出面密度与体密度之间关系式。采用二维半导体自由载流子面密度表示式和范德堡 -霍尔实验测量在衬底 Ga As上 MBE生长的 Q2 D的样品 Ga Sb和 In As1-x Sbx ( x≈ 0 .2 2 )禁带宽度 Eg,获得满意结果。     

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.     

Improved optical performance of GaN grown on pattered sapphire substrate

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 (10(1)2) plane are as low as 312.80 arcsec and 298.08 acrsec, respec-tively. 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.     

Surface morphology and electronic properties of dislocations in AlGaN/GaN heterostructures

Scanning force microscopy was used to examine the surfaces of AlGaN/GaN heterostructures grown by molecular beam epitaxy (MBE) on GaN templates prepared by hydride vapor phase epitaxy (HVPE). Away from dislocations, the MBE growth replicates the surface morphology of the HVPE film, with monolayer steps clarly visible in topographic images. However, the surface morphology near dislocations depends strongly on the MBE growth conditions. Under Ga rich growth the dislocations appear as hillocks, while under stoichiometric growth they appear as pits. A dependence on Al concentration is also observed. Surface contact potential variation near dislocations is consistent with excess negative charges surrounding by a depletion region, but this was observed only for the film grown under stoichiometric conditions.     

湿法化学腐蚀法估算GaN外延层中位错密度

研究了采用熔融NaOH对MOCVD生长的GaN外延层的湿法腐蚀结果,结合原子力显微镜表征其腐蚀坑形貌及腐蚀坑密度,得出了优化的腐蚀条件.通过与熔融KOH腐蚀结果对比分析发现,熔融NaOH腐蚀速率平缓,表面更平整,腐蚀坑更规则且密度更大.结合两种腐蚀结果,可以初步得出,熔融NaOH对GaN中刃型分量位错敏感,而熔融KOH对螺型分量位错更敏感,两种腐蚀剂相结合能够更完整地揭示GaN内部位错.     

Influence of crystalline defects on transport properties of GaN grown by ammonia-molecular beam epitaxy and magnetron sputter epitaxy

GaN layers have been grown using an MBE/MSE (molecular beam epitaxy/magnetron sputter epitaxy) dual-mode system. The layers grown by the two techniques exhibited a large difference in crystalline quality and presented a broad spectrum of structural, optical, and transport properties that are useful for an analysis of the role of crystalline defects in GaN epilayers. The model of electron scattering by charged threading dislocations was applied in a theoretical fit of the mobility data. The theoretical fit in combination with x-ray diffraction and photoluminescence studies reveal the correlation between dislocation density, electron mobility, doping characteristics and yellow luminescence.     

Reduction of Dislocation Density in HVPE-Grown GaN Epilayers by Using In Situ-Etched Porous Templates

In this paper, a method was demonstrated to reduce the dislocation density of GaN film grown by hydride vapor phase epitaxy (HVPE) on an in situ selective hydrogen-etched GaN/sapphire template. The dislocations regions were etched by hydrogen to form cavities. The porous structure was formed on the GaN template grown by metal organic chemical vapor deposition after in situ hydrogen etching. The etching condition was optimized by modulating the etching temperature, pressure, and etching time. Two-step buffer layer growth and high temperature GaN film deposition were carried on the porous template. The growth parameters were optimized to keep the porous structure unfilled. The dislocations originally located in etched cavities could not propagate to the next layer grown by HVPE. Therefore, the dislocation density could be significantly reduced. High crystal quality of GaN is obtained with a low dislocation density. The full width at half-maximum FWHM of (002) is 35 arcs, and the FWHM of (102) is 48 arcs.     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

用原子力显微镜和扫描电镜研究GaN外延层中的位错腐蚀坑

用原子力显微镜和扫描电镜相结合的方法表征了KOH腐蚀后的Si掺杂GaN外延层中的位错腐蚀坑.根据腐蚀坑的不同形状和在表面的特定位置可将其分成三种类型,它们的起源可由一个关于腐蚀机制的模型加以解释.纯螺位错易于沿着由它结束的表面阶梯被腐蚀,形成一个小的Ga极性面以阻止进一步的纵向腐蚀,因而其腐蚀坑是位于两个表面阶梯交结处的截底倒六棱椎.纯刃位错易于沿位错线被腐蚀,因而其腐蚀坑是沿着表面阶梯分布的尖底倒六棱椎.极性在GaN的腐蚀过程中起了重要作用.     

AlGaN缓冲层结构对Si基GaN材料性能的影响

Si衬底与GaN之间较大的晶格失配和热失配引起的张应力使GaN外延层极易产生裂纹,如何补偿GaN所受到的张应力是进行Si基GaN外延生长面临的首要问题.采用金属有机化合物化学气相沉积(MOCVD)技术在4英寸(1英寸=2.54 cm)Si (111)衬底上制备了GaN外延材料并研究了不同AlGaN缓冲层结构对Si基GaN外延材料性能的影响,并采用高分辨X射线衍射仪(HRXRD)、原子力显微镜(AFM)、喇曼光谱以及光学显微镜对制备的GaN材料的性能进行了表征.采用3层A1GaN缓冲层结构制备了表面光亮、无裂纹的GaN外延材料,其(002)晶面半高宽为428 arcsec,表面粗糙度为0.194 nm.结果表明,采用3层A1GaN缓冲层结构可以有效地降低GaN材料的张应力和位错密度,进而遏制表面裂纹的出现,提高晶体质量.     

Recovery of Dry Etching–Induced Damage in <Emphasis Type="Italic">n</Emphasis>-GaN by Nitrogen Plasma Treatment at Growth Temperature

The n-GaN films grown by metal-organic chemical vapor deposition (MOCVD) are etched in an inductively coupled plasma (ICP) reactor chamber. Atomic-force microscopy (AFM) characterization shows an increase of the surface roughness after the etching. Furthermore, Hall measurement and photoluminescence (PL) spectra highlight deterioration of the electrical and optical properties, respectively. Attempts to recover the damage are carried out by nitrogen plasma treatments accompanied by thermal annealing at the growth temperature in a molecular-beam epitaxy (MBE) chamber. Improved electrical and optical properties compared with those of the as-etched GaN, evidenced in both Hall and PL measurements, show a pronounced decrease of the damage introduced by the ICP etching.