Localized-states quantum confinement induced by roughness in CdMnTe/CdTe heterostructures grown on Si(111) substrates

This work shows that despite a lattice mismatch of almost 20%, CdMnTe/CdTe/CdMnTe heterostructures grown directly on Si(111) have surprisingly good optical emission properties. The investigated structures were grown by molecular beam epitaxy and characterized by scanning transmission electron microscopy, macro-and micro-photoluminescence. Low temperature macro-photoluminescence experiments indicate three emission bands which depend on the CdTe layer thickness and have different confinement characteristics. Temperature measurements reveal that the lower energy emission band (at 1.48 eV)is associated to defects and bound exciton states, while the main emission at 1.61 eV has a weak 2D character and the higher energy one at 1.71 eV has a well-defined (zero-dimensional, 0D) 0D nature. Micro-photoluminescence measurements show the existence of sharp and strongly circularly polarized (up to 40%) emission lines which can be related to the presence of Mn in the heterostructure. This result opens the possibility of producing photon sources with the typical spin control of the diluted magnetic semiconductors using the low-cost silicon technology.

Preparation of 50mm 3C-SiC/Si(111) as Substrates Suited for Ⅲ-Nitrides

mm SiC films with high electrical uniformity a re grown on Si(111) by a newly developed vertical low-pressure chemical vapor dep osition (LPCVD) reactor.Both in-situ n- and p-type doping of 3C-SiC are achi eved by intentional introduction of ammonia and boron into the precursor gases.T he dependence of growth rate and surface morphology on the C/Si ratio and optimi zed growth conditions is obtained.The best electrical uniformity of 50mm 3C-SiC films obtained by non-contact sheet resistance measurement is ±2.58%.GaN fil ms are grown atop the as-grown 3C-SiC/Si(111) layers using molecular beam epit axy (MBE).The data of both X-ray diffraction and low temperature photoluminesc e nce of GaN/3C-SiC/Si(111) show that 3C-SiC is an appropriate substrate or buff er layer for the growth of Ⅲ-nitrides on Si substrates with no cracks.

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si(111) substrate with AlGaN interlayer

We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single A1GaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si （111） substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlCaN interlayer on the structural properties of the resulting CaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AIGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.

Preparation of LiNbO_3 films on Si(111) substrates by a modified sol-gel process

The preparation of LiNbO 3 films on Si substrates was improved by adding CH 3CH 2OH solution containing a little water to the sol of LiNb(OC 2H 5) 6. The crystallization behavior of LiNbO 3 films on Si (111) substrates was studied and completely c axis oriented LiNbO 3 films were obtained. Such factors as the hydrogen termination of silicon surface, the RTP annealing process used, the unidirectional heat flow and the preheating temperature were taken into consideration while the crystallization of c axis oriented films was analysed. Surface morphologies of the films annealed in RTP and conventional furnaces were observed by means of AFM.

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxiai layer and Si substrate before epitaxiai growth of GaN layer. High-quality and crack-free GaN epitaxiai layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.

The Growth and Fabrication of InGaN/GaN Multi-Quantum Well Solar Cells on Si(111) Substrates

Metalorganic chemical vapor deposition of a crack-free mirror-like surface of InGaN/GaN MQWs on Si(111)substrate is demonstrated,and an InGaN/GaN MQWs solar cell device is fabricated.Photo response measurement of the solar cell devices shows that the fill factor FF=49.4%,open circuit voltage V_(oc)=0.32 V,and short circuit current J_(sc)=0.07 mA/cm^(2),under AM 1.5 G illumination.In order to analyze the influence of material quality on the performance of solar cells,XRD,SEM and Raman scattering experiments are carried out.It is found that insertion of a proper top AlN layer can effectively improve the material quality,and therefore enhance the photovoltaic performance of the fabricated device.

Preparation and characterization of GaN films grown on Ga-diffused Si (111) substrates

Hexagonal GaN films were prepared by nitriding Ga_2O_3 films with flowingammonia. Ga_2O_3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.)magnetron sputtering. This paper have investigated the change of structural properties of GaN filmsnitrided in NH_3 atmosphere at the temperatures of 850, 900, and 950 deg C for 15 min and nitridedat the temperature of 900 deg C for 10, 15, and 20 min, respectively. X-ray diffraction (XRD),scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectronspectroscopy (XPS) were used to analyze the structure, surface morphology and composition ofsynthesized samples. The results reveal that the as-grown films are polycrystalline GaN withhexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained whennitrided at 900 deg C for 15 min.

Performance improvement of Ga N-based light-emitting diodes transferred from Si(111) substrate onto electroplating Cu submount with embedded wide p-electrodes

Crack-free Ga N/In Ga N multiple quantum wells（MQWs） light-emitting diodes（LEDs） are transferred from Si substrate onto electroplating Cu submount with embedded wide p-electrodes. The vertical-conducting n-side-up configuration of the LED is achieved by using the through-hole structure. The widened embedded p-electrode covers almost the whole transparent conductive layer（TCL）, which could not be applied in the conventional p-side-up LEDs due to the electrodeshading effect. Therefore, the widened p-electrode improves the current spreading property and the uniformity of luminescence. The working voltage and series resistance are thereby reduced. The light output of embedded wide p-electrode LEDs on Cu is enhanced by 147% at a driving current of 350 m A, in comparison to conventional LEDs on Si.

Preparation of c-Axis Oriented LiNb_(1-x) Ta_xO_3 Films on Si(111) Substrates by a Modified Sol-gel Process

In this work, we succeeded in the preparation of LiNb 1- x Ta x O 3 films on Si(111) substrates by means of sol gel process, and the usual sol gel process for the preparation of LiNbO 3 and LiTaO 3 films on Si substrates was improved by adding a 33% aqueous solution of CH 3CH 2OH to the mixed sols of LiNb(OCH 2CH 3) 6 and LiTa(OCH 2CH 3) 6 . The crystallization behavior of LiNb 1- x Ta x O 3 films on Si(111) substrates has been studied. Highly c axis oriented LiNb 1- x Ta x O 3 films have been obtained within the tantalum composition range of \{0< x <0 33\}. Some factors such as the hydrogen termination of the silicon surface, the RTP annealing process that provides the unidirectional heat flow and the preheating temperature are discussed to analyze the crystallization of the c axis oriented films.

Stress Distribution in GaN Films grown on Patterned Si (111) Substrates and Its Effect on LED Performance

Crack free GaN films were grown on 1200×1200𝜈m^(2) patterned Si(111)substrates and 36 light emitting diodes(LEDs)were fabricated in each pattern unit.Spatial distribution of the tensile stress in the pattern units and its influence on the LED performance are studied by micro-Raman and electroluminescence(EL).The Raman shift of the GaN𝐹E_(2) mode shows that the tensile stress is the maximum at the center,partially relaxed at the edge,and further relaxed at the corner.With the stress relaxation,the EL wavelength has a significant blue shift and the luminous intensity shows a great enhancement.

The Influence of Graded AlGaN Buffer Thickness for Crack-Free GaN on Si(111)Substrates by using MOCVD

GaN films with different thicknesses of Al composition graded AlGaN buffer are grown on substrates of Si(111)by metal-organic chemical vapor deposition(MOCVD).The thicknesses of graded AlGaN buffer are fixed at 200 nm,300 nm,and 450 nm,respectively.Optical microscopy,atomic force microscopy,x-ray diffraction,and Raman spectroscopy are employed to characterize these samples.We find that the thickness of the graded AlGaN buffer layer plays a key role on the following growth of GaN films.The optimized thickness of the graded AlGaN buffer layer is 300 nm.Under such conditions,the GaN epitaxial film is crack-free,and its dislocation density is the lowest.

Growth of 2 um Crack-Free GaN on Si(111)Substrates by Metal Organic Chemical Vapor Deposition

A 2μm high quality crack-free GaN film was successfully grown on 2-inch Si(111)substrates by metal organic chemical vapor deposition with a high temperature AIN/graded-AlGaN multibuffer and an AIN/GaN superlattice interlayer.It is found that the structures,as well as the thicknesses of the multibuffer and interlayer,are crucial for the growth of a crack-free GaN epilayer.The GaN(0002)XRD FWHM of the crack-free sample is 479.8arcsec,indicating good crystal quality.An AlGaN/GaN heterostructure was grown and tested by Van der Pauw Hall measurement.The electron mobility of two-dimensional electron gas increases from 1928 cm^(2)/V.S to 12277cm^(2)/V s when the test-temperature decreases from room temperature to liquid nitrogen temperature.The electron mobility is comparable to that of AlGaN/GaN heterostructures grown on sapphire,and the largest value is obtained for an AlGaN/GaN/Si(111)heterostructure grown by metal organic chemical vapor deposition.

Structural and Photoluminescence Characterization of GaN Film Grown on Si(111)Substrate

GaN epilayer grown on Si(111)substrate by a novel vacuum reaction method rather than metal organic chemical vapor deposition or molecule beam epitaxy is reported.Scanning electron micrograph shows that surface of GaN film is flat and crack-free.A pronounced GaN(0002)peak appears in the x-ray diffraction pattern.The full width at half-maximum(FWHM)of the double-crystal x-ray rocking curve for(0002)diffraction from the GaN epilayer is 30arcmin.The photoluminescence spectrum shows that the GaN epilayer emits light at the wavelength of 365nm with an FWHM of 8nm(74.6meV).

Structure and Strain Properties of GaN Films Grown on Si（111） Substrates with AlxGa1-xN/AlyGa1-yN Superlattices

CaN films with an AlxGa1-xN/AlyGa1-xN superlattice （SL） buffer layer are grown on Si（111） substrates by metal-organic chemical vapor deposition （MOCVD）. The structure and strain properties of the samples are studied by optical microscopy, Raman spectroscopy, x-ray diffractometry and atomic force microscopy. The results show that the strain status and crystalline quality of the CaN layers are strongly dependent on the difference of the Al composition between AlxCa1-xN barriers and AlyCa1-yN wells in the SLs. With a large Al composition difference, the CaN film tends to generate cracks on the surface due to the severe relaxation of the SLs. Otherwise, when using a small Al composition difference, the crystalline quality of the CaN layer degrades due to the poor function of the SLs in filtering dislocations. Under an optimized condition that the Al composition difference equals 0.1, the crack-free and compressive strained CaN film with an improved crystalline quality is achieved. Therefore, the AlxGa1-xN/AlyGal-yN SL buffer layer is a promising buffer structure for growing thick CaN films on Si substrates without crack generation.

Si(111)衬底上多层石墨烯薄膜的外延生长

利用固源分子束外延(SSMBE)技术,在Si(111)衬底上沉积碳原子外延生长石墨烯薄膜,通过反射式高能电子衍射(RHEED)、红外吸收谱(FTIR)、拉曼光谱(RAMAN)和X射线吸收精细结构谱(NEXAFS)等手段对不同衬底温度(400、600、700、800℃)生长的薄膜进行结构表征.RAMAN和NEXAFS结果表明:在800℃下制备的薄膜具有石墨烯的特征,而400、600和700℃生长的样品为非晶或多晶碳薄膜.RHEED和FTIR结果表明,沉积温度在600℃以下时C原子和衬底Si原子没有成键,而衬底温度提升到700℃以上,沉积的C原子会先和衬底Si原子反应形成SiC缓冲层,且在800℃沉积时缓冲层质量较好.因此在Si衬底上制备石墨烯薄膜需要较高的衬底温度和高质量的SiC缓冲层.

Si(111)衬底上GaN的MOCVD生长

利用LP-MOCVD在S i(111)衬底上,以高温A lN为缓冲层,分别用低温GaN(LT-GaN)和偏离化学计量比富Ga高温GaN(HT-GaN)为过渡层外延生长六方相GaN薄膜。采用高分辨率双晶X射线衍射(DCXRD),扫描电子显微镜(SEM),原子力显微镜(AFM)和室温光致荧光光谱(RT-PL)进行分析。结果表明,有偏离化学计量比富Ga HT-GaN为过渡层生长的GaN薄膜质量和光致荧光特性均明显优于以LT-GaN为过渡层生长的GaN薄膜,得到GaN(0002)和(10ī2)的DCXRD峰,其半峰全宽(FWHM)分别为698 s和842 s,室温下的光致荧光光谱在361 nm处有一个很强的发光峰,其半峰全宽为44.3 m eV。

表面台阶对超高真空下Si(111)基片表面银原子吸附与重构的影响

利用真空蒸发技术制备出了良好的Si(111)-3×3-Ag和Si(111)-3×1-Ag重构表面。通过低能电子衍射法和光学表面二次谐波法研究了两种类型切割角的单晶硅基片在超高真空银蒸镀过程中表面结构随衬底温度和蒸镀量的变化情况。vicinal样品产生的弱SinPout信号表明表面台阶的存在对Si(111)-3×3-Ag表面的成核生长过程有显著影响。低能电子衍射图片显示,500℃以上的高温下两种基片表面所形成的Si(111)-3×1-Ag重构分别为类单畴和三畴结构。类单畴和三畴结构Si(111)-3×1-Ag的光学表面二次谐波SinSout信号的一致性可能揭示了Si(111)-3×1-Ag结构中孪畴结构的存在。

SiO_2/Si(111)表面Ge量子点的生长研究

Si衬底用化学方法清洗后,表面大约残余1.0 nm厚SiO2薄膜。利用原子力显微镜(AFM)和反射高能电子衍射(RHEED)来研究温度和Ge蒸发厚度对在SiO2薄膜表面生长的Ge量子点的影响。实验结果表明,当衬底温度超过500℃时,SiO2开始与Ge原子发生化学反应,并形成与Si(111)表面直接外延的Ge量子点。在650℃时,只有Ge的厚度达到0.5nm时,Ge量子点才开始形成。

Si(111)基片上Mg_2Si薄膜的脉冲激光沉积

采用脉冲激光沉积方法在Si(111)基片上制备了Mg2Si薄膜。研究了激光能量密度、退火气氛及压强、退火温度、退火时间等工艺条件对Mg2Si薄膜生长的影响。用X射线衍射仪分析了Mg2Si薄膜的物相,用原子力显微镜、高分辨场发射扫描电镜表征了薄膜的形貌。实验结果表明:在激光能量密度为2.36 J/cm2,Si(111)基片上室温、真空(真空度10-6Pa)条件下沉积,在Ar气压强为10 Pa,500℃,30 min条件下原位退火得到了纯相、结构均匀、表面平整、厚度约为900 nm的Mg2Si多晶薄膜。