MOCVD-Grown AlGaN/AlN/GaN HEMT Structure with High Mobility GaN Thin Layer as Channel on SiC

AlGaN/AlN/GaN high electron mobility transistor (HEMT) structures with a high-mobility GaN thin layer as a channel are grown on high resistive 6H-SiC substrates by metalorganic chemical vapor deposition. The HEMT structure exhibits a typical two-dimensional electron gas (2DEG) mobility of 1944cm2/(V · s) at room temperature and 11588cm2/(V· s) at 80K with almost equal 2DEG concentrations of about 1.03 × 1013 cm-2 High crystal quality of the HEMT structures is confirmed by triple-crystal X-ray diffraction analysis. Atomic force microscopy measurements reveal a smooth AlGaN surface with a root-mean-square roughness of 0. 27nm for a scan area of 10μm × 10μm. HEMT devices with 0.8μm gate length and 1.2mm gate width are fabricated using the structures. A maximum drain current density of 957mA/mm and an extrinsic transconductance of 267mS/mm are obtained.

Dislocation Reduction in GaN on Sapphire by Epitaxial Lateral Overgrowth

High quality GaN is grown on GaN substrate with stripe pattern by metalorganic chemical vapor deposition by means of epitaxial lateral overgrowth. AFM,wet chemical etching, and TEM experiments show that with a two-step ELOG procedure, the propagation of defects under the mask is blocked, and the coherently grown GaN above the window also experiences a drastic reduction in defect density. In addition, a grain boundary is formed at the coalescence boundary of neighboring growth fronts. The extremely low density of threading dislocations within wing regions makes ELOG GaN a potential template for the fabrication of nitride-based lasers with improved performance.

超低压选择区域生长法制备产生10GHz重复率超短光脉冲的级联电吸收调制器与分布反馈激光器单片集成光源

采用超低压（22×10^2Pa）选择区域生长（selective area growth，SAG）金属有机化学气相沉积（metal—organic chemical vapor deposition，MOCVD）技术成功制备了InGaAsP／InGaAsP级联电吸收调制器（electroabsorption modulator，EAM）与分布反馈激光器（distributed feedback laser，DFB）单片集成光源的新型光电器件．实验结果表明，采用该技术制备的器件具有良好的性能

双异质外延SOI材料Si/γ-Al_3O_3/Si的外延生长

利用MOCVD（metalorganic chemical vapor deposition）和APCVD（atmosphere chemical vapor deposition）硅外延技术在Si(100)衬底上成功地制备了双异质Si/γ-Al_2O_3/Si SOI材料。利用反射式高能电子衍射（RHEED）、X射线衍射（XRD）及俄歇能谱（AES）对材料进行了表征。测试结果表明，外延生长的γ-Al_2O_3和Si薄膜都是单晶薄膜，其结晶取向为（100）方向，外延层中Al与O化学配比为2:3。同时，γ-Al_2O_3外延层具有良好的绝缘性能，其介电常数为8.3，击穿场强为2.5MV/cm。AES的结果表明，Si/γ-Al_2O_3/Si双异质外延SOI材料两个异质界面陡峭清晰。

Effects of polarization field on formation of two-dimensional electron gas in (0001) and (11(2)over-bar0) plane AlGaN/GaN heterostructures

Photoluminescence (PL) and temperature-dependent Hall effect measurements were carried out in (0001) and (11 (2) over bar0) AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. There are strong spontaneous and piezoelectric electric fields (SPF) along the growth orientation of the (0001) AlGaN/GaN heterostructures. At the same time there are no corresponding SPF along that of the (1120) AlGaN/GaN. A strong PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes was observed at 3.258 eV at room temperature in (0001) AlGaN/GaN heterointerfaces while no corresponding PL peak was observed in (11 (2) over bar0). The existence of a 2DEG was observed in (0001) AlGaN/GaN multi-layers with a mobility saturated at 6000 cm(2)/V s below 80 K, whereas a much lower mobility was measured in (11 (2) over bar0). These results indicated that the SPF was the main element to cause the high mobility and high sheet-electron-density 2DEG in AlGaN/GaN heterostructures. (C) 2004 Elsevier B.V. All rights reserved.

Coupled AlxGa1-xAs-AlAs distributed Bragg reflectors for high brightness AlGaInP light emitting diodes

A novel coupled distributed Bragg reflector (DBR) with double thickness periods was theoretically analyzed based on the spontaneous radiation properties of high brightness AlGaInP light emitting diodes(LED). Several important factors were considered including spontaneous radiation angle distribution, absorption and FTR of DBR. Calculation results showed that the optimum optical thickness of single layer of the DBR deviates from 1/4 lambda. AIGaInP high brightness light emitting diodes both with Al0.5Ga0.5As/AlAs coupled DBR and with conventional DBR were fabricated by metalorganic chemical vapor deposition(MOCVD). X-ray double crystal diffraction and reflection spectrum were employed to determine the thickness and reflectivity of the DBR. It was found that reflectivity of coupled DBR is less sensitive to incident angle than conventional DBR, higher external quantum efficiency of light emitting diodes with coupled DBR was obtained than that with conventional DBR.

High brightness AlGaInP orange light emitting diodes

Orange AlGaInP high brightness light emitting diodes (LEDs) were fabricated by low pressure metalorganic chemical vapor deposition(LP-MOCVD) technology. AlGaInP double heterojunction structure was used as active layer. 15 pairs of Al0.5Ga0.5As/AlAs distributed Bragg reflector and 7 mu m Al0.8Ga0.2As current spreading layer were employed to reduce the absorption of GaAs substrate and upper anode respectively. At 20mA the LEDs emitting wavelength was between 600-610nm with 18.3nm FWHM, 0.45mW radiation power and 1.7% external quantum efficiency. Brightness of the LED chips and LED lamps with 15 degrees viewing angle(2 theta(1/2)) reached 30mcd and 1000mcd respectively.

Growth and fabrication of high performance 980nm strained InGaAs quantum well lasers using novel hybrid material system of InGaAsP and AlGaAs

In this paper, we report on the design, growth and fabrication of 980nm strained InGaAs quantum well lasers employing novel material system of Al-free active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in laser structure design, improvement of surface morphology and laser performance. We demonstrate an optimized broad-waveguide structure for obtaining high power 980nm quantum well lasers with low vertical beam divergence. The laser structure was grown by low-pressure metalorganic chemical vapor deposition, which exhibit a high internal quantum efficiency of similar to 90% and a low internal loss of 1.5-2.5 cm(-1). The broad-area and ridge-waveguide laser devices are both fabricated. For 100 mu m wide stripe lasers with cavity length of 800 mu m, a low threshold current of 170mA, a high slope efficiency of 1.0W/A and high output power of more than 3.5W are achieved. The temperature dependences of the threshold current and the emitting spectra demonstrate a very high characteristic temperature coefficient (T-o) of 200-250K and a wavelength shift coefficient of 0.34nm/degrees C. For 4 mu m-width ridge waveguide structure laser devices, a maximum output power of 340mW with GOD-free thermal roll-over characteristics is obtained.

Study of infrared luminescence from Er-implanted GaN films

In this study, we report the dependences of infrared luminescence properties of Er-implanted GaN thin films (GaN:Er) on the kinds of substrates used to grow GaN, the growth techniques of GaN, the implantation parameters and annealing procedures. The experimental results showed that the photoluminescence (PL) intensity at 1.54 mum was severely influenced by different kinds of substrates. The integrated PL peak intensity from GaN:Er /Al2O3 (00001) was three and five times stronger than that from GaN:Er /Si (111) grown by molecular beam epitaxy (MBE) and by metalorganic chemical vapor deposition (MOCVD), respectively. The PL spectra observed from GaN:Er/Al2O3 (0001) grown by MOCVD and by MBE displayed a similar feature, but those samples grown by MOCVD exhibited a stronger 1.54 mum PL. It was also found that there was a strong correlation between the PL intensity with ion implantation parameters and annealing procedures. Ion implantation induced damage in host material could be only partly recovered by an appropriate annealing temperature procedure. The thermal quenching of PL from 15 to 300 K was also estimated. In comparison with the integrated PL intensity at 15 K, it is reduced by only about 30 % when going up to 300 K for GaN:Er/Al2O3 sample grown by MOCVD. Our results also show that the strongest PL intensity comes from GaN:Er grown on Al2O3 substrate by MOCVD. (C) 2004 Elsevier B.V. All rights reserved.

High power 980 nm Al-free strained quantum-well lasers for erbium-doped fiber amplifiers

In this paper, we reported on the fabrication of 980 nm InGaAs/InGaAsP strained quantum-well (QW) lasers with broad waveguide. The laser structure was grown by low-pressure metalorganic chemical vapor deposition on a n(+)- GaAs substrate. For 3 mu m stripe ridge waveguide lasers, the threshold current is 30 mA and the maximum output power and the output power operating in fundamental mode are 350 mW and 200 mW, respectively. The output power from the single mode fiber is up to 100 mW, the coupling efficiency is 50%. We also fabricated 100 mu m broad stripe coated lasers with cavity length of 800 mu m, a threshold current density of 170 A/cm(2), a high slope efficiency of 1.03 W/A and a far-field pattern of 40 x 6 degrees are obtained. The maximum output power of 3.5 W is also obtained for 100 mu m wide coated lasers. (C) 2000 Elsevier Science B.V. All rights reserved.

激光热处理对化学沉积Ni-P合金薄膜性能的影响

用扫描电镜(SEM)观察了化学沉积Ni-P合金薄膜/单晶硅基体的结构与颗粒度,利用X射线衍射(XRD)技术测试了其化学沉积后的残余应力,测量了激光热处理后残余应力的变化规律,分析了残余应力对磨损性能及界面结合强度的影响。实验结果表明,化学沉积Ni-P合金薄膜/硅基体的残余应力均表现为拉应力,经过激光热处理后残余应力发生了变化,由高值的拉应力变为低值的拉应力或压应力；薄膜残余应力对其磨损性能有明显的影响,其磨损量随着残余应力的减小而减小；薄膜与基体结合强度随着残余应力的增大而减小,合理地选择激光热处理参数可

Photoluminescence from heterogeneous SiGe/Si nanostructures prepared via a two-step approach strategy

A two-step approach of preparation for SiGe/Si heterogeneous nanostructures, which combined with ultra-high vacuum chemical deposition and electrochemical anodization techniques, is demonstrated. Uniformly distributed nanostructures with a quite uniform distribution of size and morphology are obtained. A strong room-temperature photoluminescence from the nanostructures was observed with a narrow full-width at half-maximum of around 110 meV. The possible origins of the two main peaks at around 1.6 and 1.8 eV have been discussed in detail. The two-step approach is proved to be a promising method to fabricate new Si-based optoelectronic materials. (C) 2009 Elsevier B.V. All rights reserved.

Improvement of GaN-based light emitting diodes performance grown on sapphire substrates patterned by wet etching - art. no. 684107

An effective approach to enhance the light output power of InGaN/GaN light emitting diodes (LED) was proposed using pyramidal patterned sapphire substrates (PSS). The sapphire substrates were patterned by a selective chemical wet etching technique. GaN-based LEDs were fabricated on patterned sapphire substrates through metal organic chemical deposition (MOCVD). The LEDs fabricated on patterned sapphire substrates exhibit excellent device performance compared to the conventional LEDs fabricated on planar sapphire substrates in the case of the same growth and device fabricating conditions. The light output power of the LEDs fabricated on patterned sapphire substrates was about 37% higher than that of LEDs on planar sapphire substrates at an injection current of 20 mA. The significant enhancement is attributable to the improvement of the quality of GaN-based epilayers and improvement of the light extraction efficiency by patterned sapphire substrates.

PHOTOLUMINESCENCE AND SURFACE PHOTOVOLTAIC SPECTRA OF STRAINED INP ON GAAS

A high energy shift of the band-band recombination has been observed in the photoluminescence (PL) spectra of the strained InP epilayer on GaAs by metalorganic chemical vapor deposit. The strain determined by PL peak is in good agreement with calculated thermal strain. The surface photovoltalic spectra gives the information about energy gap, lattice mismatching, and composition of heteroepilayers, diffusion length, surface, and interface recombination velocity of minority carriers of heteroepitaxy layers.

Growth of Cubic GaN by MOCVD at High Temperature

High quality cubic GaN (c-GaN) is grown by metalorganic vapor deposition (MOCVD) at an increased growth temperature of 900 ℃, with the growth rate of 1.6 μm/h. The full width at half maximum (FWHM) of room temperature photoluminescence (PL) for the high temperature grown GaN film is 48meV. It is smaller than that of the sample grown at 830 ℃. In X-ray diffraction (XRD) measurement, the high temperature grown GaN shows a (002) peak at 20° with a FWHM of 21'. It can be concluded that, although c-GaN is of metastable phase, high growth temperature is still beneficial to the improvement in its crystal quality. The relationship between the growth rate and growth temperature is also discussed.