Effect of growth stoichiometry on the structural properties of AlN films on thermally nitrided sapphire $(11\bar 20)$

High‐quality AlN epilayers were grown via pulsed sputtering deposition on thermally nitrided sapphire $(11\bar 20)$ with precise control of the N/Al ratio. Under slightly Al‐rich growth conditions, the growth of AlN epilayers on the thermally nitrided sapphire proceeded in a two‐dimensional mode from the initial stage of growth, and their surfaces were atomically flat stepped and terraced structures. The FWHM values of the X‐ray rocking curves were as low as 87 arcsec and 339 arcsec for the 0002 and $1 \bar 102$ diffractions, respectively, at a film thickness of 400 nm. The present approach is therefore quite promising for the low‐cost fabrication of AlGaN‐based UV optical devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition

The effect of Al incorporation on the AlGaN growth by metalorganic chemical vapor deposition is investigated. With the increase of trimethylalluminum (TMAl) flux, the crystal quality becomes worse, and the epilayer surface becomes rougher. An interesting phenomenon is that the growth rate of AlGaN decrease with increasing TMAl flux, which is opposite to the AlN growth rate dependence on the TMAl flux. All these effects are attributed to the different properties of Al atoms due to the higher bond strength of Al-N compared with Ga-N, which lead to lower surface mobility and stronger competitive ability of Al atoms during the growth. The enhancement of the surface mobility of Al is especially important for improving the quality of AlGaN.     

H<Subscript>2</Subscript>O<Subscript>2</Subscript>-molecular beam epitaxy of high quality ZnO

We have studied the growth and characterization of ZnO epilayers on (0001)-sapphire by H₂O₂-molecular beam epitaxy (MBE). A high temperature (HT) MgO buffer followed by a low-temperature ZnO buffer was introduced in order to accommodate the lattice mismatch between ZnO and sapphire. The surface morphology of the samples was studied using atomic force microscopy (AFM), and scanning electron microscopy (SEM). The crystalline quality of the layers was investigated by employing high resolution X-ray diffractometry (HRXRD) and high resolution transmission electron microscopy (HRTEM). The electrical properties of the grown ZnO layers were studied by Hall-effect measurements in a standard van der Pauw configuration. The measured surface roughness for the best layers is as low as 0.26 nm rms. HRXRD measurements of the obtained ZnO layers show excellent quality of the single crystalline ZnO heteroepitaxially grown on (0001)-sapphirewith a HT MgO buffer layers. The influence of the growth conditions on the crystalline quality is discussed. The FWHM of the HRXRD (0002) rocking curves measured for the 2-inch ZnO-on-sapphire is as low as 27 arcsec with a very high lateral homogeneity across the whole 2-inch ZnO epilayers. The results indicate that H₂O₂-MBE is a suitable technique to fabricate ZnO epilayers of very high quality. PACS 61.10.Nz; 68.37.Lp; 81.05.Dz; 81.15.Hi     

Polarity control in MBE growth of III-nitrides,and its device application

Until recently, molecular beam epitaxy (MBE) has been behind metalorganic chemical vapor deposition (MOCVD) as a growth technique for III-nitride thin films, due to the lack of nitrogen source powerful enough for the growth in vacuum and the understanding of growth mechanism. We have clarified that the quality of GaN epilayers on sapphire substrates grown by N2 plasma-assisted MBE can be much improved by realizing Ga-polarity growth mode, which enables us to fabricate HFETs using the MBE-grown AIGaN/GaN 2DEG structures. The Ga-polarity growth mode was found to be achieved by Al high temperature buffer process, In flux exposure etc., and directly confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS) technique. The relation between the surface reconstruction structure of GaN epilayers and the lattice polarity of the epilayers is also shown.     

In气氛下晶体生长对Mg掺杂p-Al_xGa_(1-x)N激活能的影响

Ⅲ-Ⅴ族氮化物宽禁带半导体材料体系中,普通方法生长的p型外延层电导率一般都很低,成为了制约器件性能提高的瓶颈。在p-AlxGa1-xN材料中,Mg受主的激活能较大,并且随Al组份增加而增大。通过在p-AlxGa1-xN材料生长过程中引入三甲基铟(TMIn),发现能有效地降低AlxGa1-xN材料中受主态的激活能。为研究不同In气氛下生长的p-AlxGa1-xN材料的性质,在使用相同二茂基镁(CP2Mg)的情况下,改变TMIn流量,生长了A,B,C和D四块样品。X射线衍射(XRD)组份分析表明:在1100℃下生长AlxGa1-xN外延层时,In的引入不会影响晶体组份。利用变温霍尔(Hall)测试研究了p-AlxGa1-xN材料中受主的激活能,结果表明:In气氛下生长的外延层相比无In气氛下生长的外延层,受主激活能明显降低,电导率显著提高。采用这种方法改进深紫外发光二极管(LED)的p-AlxGa1-xN层后,LED器件性能明显提高。     

Investigation of AlN growth on sapphire substrates in a horizontal MOVPE reactor

AlN growth was performed on c-plane sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) using trimethylaluminium (TMAl) and ammonia. The influence of the carrier gases H₂ and N₂ and their mixtures on the surface morphology and structural characteristics was investigated as well as the influence of the growth temperature of the total source partial pressure and of the TMAl substrate pretreatment. It was found that smoother layers and better structural characteristics are obtained for lower source partial pressures. Decreasing of growth temperature led to improvement of surface morphology, and increasing of nitrogen in gas phase led to improvement structural quality of the layer. A pretreatment of the substrate leads to rougher layers.     

Growth of high material quality InAs/GaSb type-II superlattice for long-wavelength infrared range by molecular beam epitaxy

By optimizing the V/III beam-equivalent pressure ratio, a high-quality InAs/GaSb type-II superlattice material for the long-wavelength infrared (LWIR) range is achieved by molecular beam epitaxy (MBE). High-resolution x-ray diffraction (HRXRD), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectrometer are used to characterize the material growth quality. The results show that the full width at half maximum (FWHM) of the superlattice zero-order diffraction peak, the mismatching of the superlattice zero-order diffraction peak between the substrate diffraction peaks, and the surface roughness get the best results when the beam-equivalent pressure (BEP) ratio reaches the optimal value, which are 28 arcsec, 13 arcsec, and 1.63 Å, respectively. The intensity of the zero-order diffraction peak is strongest at the optimal value. The relative spectral response of the LWIR detector shows that it exhibits a 100% cut-off wavelength of 12.6 μm at 77 K. High-quality epitaxial materials have laid a good foundation for preparing high-performance LWIR detector.     

Adsorption and decomposition of ammonia on W(100); XPS and UPS studies

The adsorption and decomposition of ammonia on a clean and c(2 × 2)-N ordered W(100) surface has been studied by photoemission spectroscopy (XPS and UPS). At 120 K molecularly adsorbed ammonia was identified by N(1s) core level emission at 400.9 eV and the valence emissions at 7.6 and 11.7 eV. By heating the sample stepwise the N(1s) core level shifted to lower binding energy. In the valence region, the corresponding spectral changes were obtained, where the dependence of the peak intensity on photon energy was observed. These observations were interpreted to demonstrate that adsorbed ammonia dissociates its hydrogen successively to form NH_x(a) and finally to atomic nitrogen. On the other hand, ammonia was molecularly adsorbed on a c(2 × 2)-N ordered surface even at temperatures as high as 300 K, although the spectra at 400 K or above were very similar to those under a steady state flow condition, where the tungsten surface was mostly covered by atomic nitrogen. At higher ammonia pressure up to about 100 Pa thicker nitride layers were formed at 700 K, which were characterized by the N(1s) core level at 397.3 eV and a broad emission around 6 eV in the valence level.     

Plasma assisted molecular beam epitaxial growth of GaN with low growth rates and their properties

A systematic investigation on PA-MBE grown GaN with low growth rates(less than 0.2μm/h)has been conducted in a wide growth temperature range,in order to guide future growth of sophisticated fine structures for quantum device applications.Similar to usual growths with higher growth rates,three growth regions have been revealed,namely,Ga droplets,slightly Ga-rich and N-rich 3D growth regions.The slightly Ga-rich region is preferred,in which GaN epilayers demonstrate optimal crystalline quality,which has been demonstrated by streaky RHEED patterns,atomic smooth surface morphology,and very low defect related yellow and blue luminescence bands.The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window(~700-760℃)has been identified.The growth rate shows a strong dependence on growth temperatures in the optimal temperature window,and attention must be paid when growing fine structures at a low growth rate.Mg and Si doped GaN were also studied,and both p-and n-type materials were obtained.     

高质量InGaN的等离子体辅助分子束外延生长和In的反常并入行为

采用射频等离子体辅助分子束外延技术生长得到了In组分精确可控且高质量的In_xGa_1-xN (x ≤ 0.2) 外延薄膜. 生长温度为580 ℃的In_0.19Ga_0.81N薄膜(10.2) 面非对称衍射峰的半高宽只有587弧秒, 背景电子浓度为3.96× 10¹⁸/cm³. 在富金属生长区域, Ga束流超过N的等效束流时, In组分不为零, 即Ga并没有全部并入外延层; 另外, 稍微增加In束流会降低InGaN的晶体质量. 关键词： InGaN 外延薄膜 射频等离子体辅助分子束外延 In 并入 晶体质量     

Growth mode and effect of carrier gas on In0.53Ga0.47As/InP surface morphology grown with trimethylarsine and arsine

Different growth mode have been observed for InGaAs/InP grown with trimethylarsine and arsine by Metalorganic Vapor Phase Epitaxy (MOVPE) when changing the carrier gas. The surface has been investigated by Atomic Force Microscope (AFM) for epilayers grown at 600°C under pure hydrogen or a mixture of hydrogen and nitrogen as carrier gas. The step/terrace surface morphology was observed for InP/InP and InGaAs/InP (001) using 0.2° off substrates. InP epilayers grown under nitrogen flow show step-bunched terraces as large as 170 nm. The effect of the group V source for InGaAs/InP has been studied. It is shown that the step edge characteristic of step flow growth appears for lattice-matched InGaAs/InP grown with arsine. When using TMAs and hydrogen as a carrier gas, the growth mode and surface roughness depends greatly on V/III ratio and growth temperature. Under nitrogen flow with the combination of TMI+TMG+TMAs, pit-like defects (5–8 nm deep) are visible at high surface concentration (10⁹–10¹⁰/cm²). When increasing V/III ratio, 3D growth occurs simultaneously with pit-like defects, recovering the whole surface of the sample. Various surface morphology characteristics of InGaAs epilayers assessed by AFM characterisation will be presented and discussed.     

Surface morphology and optical properties of ZnO epilayers grown on Si(1 1 1) by metal organic chemical vapor deposition

Heteroepitaxial ZnO epilayers were grown on Si(1 1 1) substrates using a vertical geometry atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD) system. The growth temperature was varied from 550 °C to 650 °C in steps of 25 °C. The ZnO growth rate and surface morphology were strong functions of the growth temperature and ranged from ∼0.16 μm/h to 1.36 μm/h. The surface morphology of the ZnO films changed from granular to sharp tips as the growth temperature increased. The effect of buffer thickness was also examined, and was found to have a strong effect on the optical properties of the ZnO. An optimized growth condition for ZnO epilayers was found at 625 °C, producing a FWHM in the room temperature photoluminescence (PL) spectrum of 4.5 nm and a preferred growth orientation along the (0 0 2) direction.Transmission electron microscopy images and selected area diffraction patterns showed excellent crystalline quality of both the buffer and ZnO overlayer. When non-optimized growth temperatures were employed, post-growth annealing was found to greatly enhance the ratio of band-edge to deep level emission.     

Characterization of surface deformation around Vickers indentations in InGaAsP epilayers on InP substrate

The deformation surrounding Vickers indentations on InGaAsP/InP epilayers have been studied in detail. The surface topography was characterized by using atomic force microscopy (AFM). The material pile-up and sink-in regions around the indentation impression was observed for the quaternary InGaAsP/InP epilayers. The sectional analysis mode of the AFM shows the depth profile at the indented region. Microindentation studies were carried out for different atomic fraction of the quaternary InGaAsP/InP compound semiconductor alloys. The microhardness values of InGaAsP/InP epilayers were found to be in the range of 5.08 and 5.73 GPa. These results show that the hardness value of the quaternary alloy drastically increases as the composition of As was increased by 0.01 atomic fraction and when the phosphorous concentration decreases from 0.4 to 0.38. The reason may be that the increase in As concentration hardens the lattice when phosphorous concentration was less and hardness decreases when phosphorous was increased.     

Atomically smooth interfaces of type-II InAs/GaSb superlattice on metamorphic GaSb buffer grown in 2D mode on GaAs substrate using MBE

In the paper, the comparative analysis of type-II InAs/GaSb SLs deposited on three types of GaSb buffers: homoepitaxial, metamorphic and one grown using the interfacial misfit (IMF) array technique has been presented. The buffer layers as well as superlattices were grown under nominally identical technological conditions. HRXRD investigations proved better crystal quality of the metamorphic material than the IMF-GaSb. FWHM_RC were equal to 156 arcsec and 196 arcsec, respectively. The surface roughness of about 1?ML and 4?MLs was obtained using the atomic force microscope for 4.0?μm–metamorphic GaSb and 1.5?μm-IMF-GaSb layers, respectively. The etch pits density for both buffers was similar, 1–2?×?10⁷?cm^?2. Superlattice with 500 periods deposited on the homoepitaxial buffer was used as a reference of the best crystal quality. HRTEM images revealed straight InAs/GaSb interfaces with 1?ML thicknesses in this sample. The interfaces in SL deposited on IMF-GaSb buffer were undulated and smeared over 3?MLs. The use of the metamorphic buffer resulted in 1–2?ML straight InAs/GaSb interfaces. The main reason for this is the roughness of IMF-GaSb buffer with mounds on the surface. Based on the obtained results we have demonstrated the advantage of metamorphic approach over IMF growth mode in GaSb/GaAs material system. A two times thicker buffer could be the price worth paying for high quality structures, even when working in the production mode.     

The effects of sapphire nitridation on GaN growth by metalorganic chemical vapour deposition

In situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above a low-temperature GaN buffer layer on a c-plane sapphire substrate by metalorganic chemical vapour deposition. It is found that the lateral growth of the GaN islands and their coalescence are promoted in the initial growth stage if optimized nitridation time and temperature are selected when the substrate is pre-exposed to ammonia. As confirmed by atomic force microscopy observations, the quality of the GaN epilayers is closely dependent on the surface morphology of the nitridated buffer layer, especially grain size and nucleation density.     

截止波长12 μm的p型-InAs0.04Sb0.96材料的熔体外延生长

为了获得p-型的长波长InAsSb材料并研究掺杂剂Ge对材料特性的影响,用熔体外延法生长了掺Ge的波长为12 μm的p型-InAsSb 外延层.用傅里叶红外光谱仪、Van der Pauw 法和电子探针微分析研究了材料的透射光谱、电学性质以及组分的分布.结果表明,两性杂质Ge在熔体外延生长的InAs0.04Sb0.96材料中起受主杂质作用.当外延层的组分相同时,材料的截止波长不随掺Ge浓度的变化而变化,但是随着外延层中掺Ge量的增加,外延层的透射率下降.掺杂原子Ge在外延层的表面及生长方向的分布都是相当均匀的.77 K下测得,载流子浓度为9.18×1016 cm－3的掺Ge的p型-InAs0.04Sb0.96样品,其空穴迁移率达到1 120 cm2·Vs－1.     

氮化铝单晶薄膜的ECR PEMOCVD低温生长研究

采用电子回旋共振等离子体增强金属有机物化学气相沉积（ECR－PEMOCVD）技术，在c轴取向的蓝宝石即α Al2O3（0001）衬底上，以氮化镓（GaN）缓冲层和外延层作为初始层，分别以高纯氮气（N2）和三甲基铝(TMAl)为氮源和铝源低温生长氮化铝（AlN）薄膜.并利用反射高能电子衍射（RHEED）、原子力显微镜（AFM）和x射线衍射（XRD）等测量结果，研究了氢等离子体清洗、氮化和GaN初始层对六方AlN外延层质量的影响，从而获得解理性与α Al2O3衬底一致的六方相AlN单晶薄膜，其XRD半高宽为1 关键词： AlN 氢等离子体清洗 氮化 GaN     

Growth of GaN epitaxial layers on sapphire with preheated ammonia and their structural and optoelectronic properties

GaN epitaxial layers were grown by metalorganic chemical vapor deposition with preheated ammonia as a group V source. The growth rates of GaN epilayers were little affected when ammonia preheater temperature was varied from room temperature to 1000 °C, however, their electrical properties as well as source materials utilization efficiency was significantly improved by using preheated ammonia. GaN epilayers grown with preheated ammonia showed excellent structural and optical properties.     

Very high crystalline quality of thick 4H‐SiC epilayers grown from methyltrichlorosilane (MTS)

200 µm thick 4H‐SiC epilayers have been grown by chloride‐based chemical‐vapor deposition using methyltrichlorosilane (MTS) as single precursor. The very high crystalline quality of the grown epilayer is demonstrated by high resolution X‐Ray Diffraction rocking curve with a full‐width‐half‐maximum value of only 9 arcsec. The high quality of the epilayer is further shown by low temperature photoluminescence showing strong free exciton and nitrogen bound exciton lines. The very high crystalline quality achieved for the thick epilayer grown in just two hours at 1600 °C suggests that MTS is a suitable precursor molecule for SiC bulk growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

InGaAsSb/InP的MBE生长及特性

研究了InP基InGaAsSb外延材料受生长温度和Ⅴ/Ⅲ比的影响。实验中利用高能电子衍射(RHHEED)监测获得了合适的生长温度和Ⅴ/Ⅲ比,采用扫描电子显微镜 (SEM)、X射线光电子能谱(XPS)、X射线双晶衍射(XRDCD)和光致发光(PL)谱等方法研究了InGaAsSb薄膜材料的表面形貌、结晶质量和发光特性。通过控制生长温度和Ⅴ/Ⅲ比,获得了X射线衍射峰半峰全宽较窄的高质量的外延材料。