Yang Ruixia

Photoelectric characteristics of CH3NH3PbI3/p-Si heterojunction*

Organic–inorganic hybrid perovskite CH3NH3PbI3 film is prepared on p-type silicon substrate using the one-step solution method to form a CH3NH3PbI3/p-Si heterojunction. The film morphology and structure are characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The photoelectric properties of the CH3NH3PbI3/p-Si heterojunction are studied by testing the current–voltage (I–V) with and without illumination and capacitance–voltage (C–V) characteristics. It turns out from the I–V curve without illumination that the CH3NH3PbI3/p-Si heterojunction has a rectifier feature with the rectification ratio over 70 at the bias of ±5 V. Also, there appears a photoelectric conversion phenomenon on this heterojunction with a short circuit current (Isc) of 0.16 μA and an open circuit voltage (Voc) of about 10 mV The high frequency C–V characteristic of the Ag/CH3NH3PbI3/p-Si heterojunction turns out to be similar to that of the metal–insulator–semiconductor (MIS) structure, and a parallel translation of the C–V curve along the forward voltage axis is found. This parallel translation means the existence of defects at the CH3NH3PbI3/p-Si interface and positive fixed charges in the CH3NH3PbI3 layer. The defects at the interface of the CH3NH3PbI3/p-Si heterojunction result in the dramatic decline of the Voc. Besides, the C–V test of CH3NH3PbI3 film shows a non-linear dielectric property and the dielectric value is about 4.64 as calculated.

Enhanced light output power in InGaN/GaN light-emitting diodes with a high reflective current blocking layer

The light output power of an InGaN/GaN light-emitting diode is improved by using a SiO2/TiO2 distributed Bragg reflector (DBR) and an Al mirror as a hybrid reflective current blocking layer (CBL). Such a hybrid reflective CBL not only plays the role of the CBL by enhancing current spreading but also plays the role of a reflector by preventing photons near the p-electrode pad from being absorbed by a metal electrode. At a wavelength of 455 nm, a 1.5-pair of SiO2/TiO2 DBR and an Al mirror (i.e. 1.5-pair DBR+Al) deposited on a p-GaN layer showed a normal-incidence reflectivity as high as 97.8%. With 20 mA current injection, it was found that the output power was 25.26, 24.45, 23.58 and 22.45 mW for the LED with a 1.5-pair DBR+Al CBL, a 3-pair DBR CBL, SiO2 CBL and without a CBL, respectively.

Surface reconstructions and reflection high-energy electron diffraction intensity oscillations during homoepitaxial growth on nonmisoriented GaAs(111)B by MBE

The growth by molecular beam epitaxy of high quality GaAs epilayers on nonmisoriented GaAs(111)B substrates is reported. Growth control of the GaAs epilayers is achieved via in situ, realtime measurement of the specular beam intensity of reflection high-energy electron diffraction (RHEED). Static surface phase maps of GaAs(111)B have been generated for a variety of incident As flux and substrate temperature conditions. The dependence of GaAs(111)B surface reconstruction phases on growth parameters is discussed. The surface reconstruction is identified to be the optimum starting surface for the latter growth of mirror-smooth epilayers. Regimes of growth conditions are optimized in terms of the static surface phase diagram and the temporal RHEED intensity oscillations.

Analytical Model and Simulation for AlGaN/GaN High Electron Mobility Transistor

Based on the charge control theory, a accurate analytical model of I-V characteristics for AlGaN/GaN high electron mobility transistor (HEMT) is presented considering the relationship between self-heating effect and polarization, electron mobility, velocity saturation, conduction band discontinuity, doping concentration, channel temperature. The comparison between simulations and physical calculation shows a good agreement. The model is simple in calculations, suitable for design of microwave device and circuit.

Uniformity of Iron-Doped Semi-Insulating InP Wafers

Abstract 50 ∼ 100 mm diameter iron-doped InP crystal was grown by in-situ phosphorous injection synthesis liquid encapsulated Czochraski (LEC) method. Samples were characterized by high speed photoluminescence (PI) mapping and Etch pit density (EPD) mapping method. The perfection of these samples were studied and compared. 100 mm diameter InP single crystals were successfully developed by rapid P-injection in-situ synthesis LEC method. The EPD across the ingot was less than 5 × 104 cm−2, which was almost equal to the crystals of diameter 50 and 76 mm. By adjusting the thermal field and ensuring the chemical stoichiometry, InP crystals of larger diameters and good performance could be developed.

A novel DMTL MEMS phase shifter

This paper results for one bit DMTL phase shifter that are designed to operate from 8-32GHz on high resistivity silicon. The periodically loaded capacitor used 4 MEMS bridges that suspended on CPW transmission line. Actuation voltage is applied between bridge and CPW transmission line. The phase shifter result in a insertion loss/return loss is better than -1.0dB/-15dB from 10.5 to 30 GHz and phase shifts of 21.1/spl deg/ at 15 GHz, and 44.3/spl deg/ at 30 GHz.

Large Signal Model of AlGaN/GaN High Electron Mobility Transistor

A accurate nonlinear large signal model was extracted in this paper. The model is capable of correctly modeling the DC characteristics of AlGaN/GaN HEMT. The parameters of model are obtained from a series of pulsed I-V characteristics and S parameters adopting the on-wafer testing technique and narrow pulse testing technology. The model is implemented in ADS software, simulations and measurements data show its availability and can be used for GaN MMIC’s designing.

Fabrication of RF-ZnO buffer for epitaxial GaN layer on Si(111) substrate

Satisfactory ZnO buffer has been fabricated through radio-frequency (RF) sputtering on Si(111) substrate. Ulteriorly, a low-temperature GaN (LT-GaN) interlayer growing on RF-ZnO/Si(111) can reduce the lattice mismatch and coefficient of thermal expansion mismatch between GaN epitaxial layer and Si(111) substrate. The optimal process conditions of RF-ZnO layer are as follows: background vacuum gets 6.0×10−4Pa; sputtering power adopts 60W; pressure of Ar gas is 1.5Pa; heating temperature of Si(111) substrate is at 200°C. The RF-ZnO buffer has the unique (0002) crystal orientation, and the roughness of ZnO layer surface gets 1nm. The surface of GaN epitaxial layer grown on LT-GaN/Si(111) substrate is smooth and crack-free.

Broadband MMIC Power Amplifier for X Band Applications

The large signal model of a PHEMT with total gate width 850μm is achieved by microwave on-wafer test and IC-CAP software, then the design and optimization of circuit are implemented by ADS software. A three-stage broadband power amplifier is designed with above model. At operation frequency from 6 to 18 GHz, the output power is over 33dBm, the power gain is higher than 19dB and the PAE is more than 25%. Otherwise, the power amplifier has better power gain flatness.

As interstitials diffusion and its effects on native defects and electrical properties of undoped LECGaAs during annealing

Annealing has been carried out at 950/spl deg/C under various As pressure for undoped(ND) semi-insulating(SI) LECGaAs. The effects of the annealing on native defects and the electrical properties were investigated. The experimental results indicate that after a annealing at 950/spl deg/C for 14h under low As pressure, the Hall mobility decreases and the resistivity increases dramatically for the samples. These changes in electrical properties are due to the generation of intrinsic acceptor defects, and the generation of the intrinsic acceptor defects originates from the outdiffusion of As interstitial at high temperature. The generation of the intrinsic acceptor defects and these changes in electrical properties can be suppressed by increasing the applied As pressure during annealing.