Improvement of 1.3-μm GaInNAs Vertical Cavity Surface Emitting Lasers Grown by MOVPE

We report the improved performance of the conventional contact 1.3 #m GalnNAs vertical cavity surface emitting lasers (VCSELs) grown by metal-organic vapour-phase epitaxy (MOVPE). A new wet etching approach was applied in the fabrication of 1.3μm GaInNAs oxide-confined VCSELs. The threshold current of single mode device is 1.0mA. The multiple mode devices show very low threshold currents below 2 mA at 5-85℃, which were the best results for 1.3μm GaInNAs VCSELs reported. Maximum single mode output power of 0.256mW and the maximum multiple mode power of 0.883mW were obtained at room temperature.     

Fabrication of Ge Nano-Dot Heterojunction Phototransistors for Improved Light Detection at 1.55μm

Heterojunction phototransistors （HPTs） with several Ge/Si nano-dot layers as the absorption region are fabricated to obtain improved light detectivity at 1.55μm. The HPT detectors are of n-p-n type with ten layers of Ge（8ML ） /Si（45nm） incorporated in the base-collector junction and are grown by an ultrahigh-vacuum chemicalvapor-deposition system. The detectors are operated with normal incidence. Because of the good quality of the grown material and fabrication process, the dark current is only 0.71pA/μm^2 under 5 V bias and the breakdown voltage is over 20 V. Compared to the positive-intrinsic-negative （PIN） reference detector with the same absorption layer, the responsivity is improved over 17 times for normal incidence at 1.55μm.     

Heteroepitaxial growth of InP/GaAs(100) by metalorganic chemical vapor deposition

Using two-step method InP epilayers were grown on GaAs(100)substrates by low-pressure metalorganic chemical vapor deposition(LP-MOCVD).X-ray diffraction(XRD)and room-temperature(RT)photolu- minescence(PL)were employed to characterize the quality of InP epilayer.The best scheme of growing InP/GaAs(100)heterostructures was obtained by optimizing the initial low-temperature(LT)InP growth conditions,investigating the effects of thermal cycle annealing(TCA)and strained layer superlattice(SLS) on InP epilayers.Compared with annealing,10-periods Ga_(0.1)In_(0.9)P/InP SLS inserted into InP epilayers can improve the quality of epilayers dramatically,by this means,for 2.6-μm-thick heteroepitaxial InP,the full-widths at half-maximum(FWHMs)of XRDωandω-2θscans are 219 and 203 arcsec,respectively,the RT PL spectrum shows the band edge transition of InP,the FWHM is 42 meV.In addition,the successful growth of InP/In_(0.53)Ga_(0.47)As MQWs on GaAs(100)substrates indicates the quality of device demand of InP/GaAs heterostructures.     

Bufferless Epitaxial Growth of GaAs on Step-Free Ge(001) Mesa

GaAs/Ge heterostructures have been employed in various semiconductor devices such as solar cells,high-performance CMOS transistors,and Ⅲ-Ⅴ/Ⅳ heterogeneous optoelectronic devices.The performance of these devices is directly dependent on the material quality of the GaAs/Ge heterostructure,while the material quality of the epitaxial GaAs layer on the Ge is limited by issues such as the antiphase domain(APD),and stacking-fault pyramids(SFP).We investigate the epitaxial growth of high-quality GaAs on a Ge(001) mesa array,via molecular beam epitaxy.Following a systematic study of the Ge terrace via an in situ scanning tunneling microscope,an atomically step-free terrace on the Ge mesa measuring up to 5 × 5 μm~2 is obtained,under optimized growth conditions.The step-free terrace has a single-phase c(4 × 2) surface reconstruction.The deposition of a high-quality GaAs layer with no APD and SFP is then achieved on this step-free Ge terrace.High-resolution transmission electron microscopy and electron channel contrast image characterizations reveal the defect-free growth of the GaAs layer on the step-free Ge mesa.Furthermore,InAs quantum dots on this GaAs/Ge mesa reveal photoluminescent intensity comparable to that achieved on a GaAs substrate,which further confirms the high quality of the GaAs layer on Ge.     

Strain Field in GaAs/GaN Wafer-Bonding Interface and Its Microstructure

The strain fields in a wafer-bonded GaAs/GaN structure are measured by electron backscatter diffraction （EBSD）. Image quality （IQ） of EBSD Kikuchi patterns and rotation angles of crystal lattices as strain sensitive parameters axe employed to chaxacterize the distortion and the rotation of crystal lattices in the GaAs-interface-GaN structure, as well as to display the strain fields. The results indicate that the influence region of the strains in the wafer-bonded GaAs/GaN structure is mainly located in GaAs side because the strength of GaAs is weaker than that of GaN. The cross-sectional image of transmission electron microscopy （TEM） further reveals the distortion and the rotation of crystal lattices induced by strains systematically.     

A Novel GaAs／InGaAs／AlGaAs Structure of Modulation—Doped Field—Effect Transistors with High Transconductances

Novel structure GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors (MODFETs) with a buried p-i-n dipole layer and a 200 nm buffer layer have been fabricated.According to the calculation,the dipole buried layer not only results in the very thin buffer layer required,but also enhances the density of two-dimensional electron gas.The measured transconductances of these MODFETs,with a gate length of 2μm and a drain-source spacing of 5μm,are as high as 320mS/mm and the measured maximum drain currents of the typical devices are higher than 500mA/mm.     

High Characteristic Temperature 1.3μm InAs/GaAs Quantum-Dot Lasers Grown by Molecular Beam Epitaxy

We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot （QD） lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.     

Photoelectric Property Improvement of 1.0-eV GaInNAs and Applications in Lattice-Matched Five-Junction Solar Cells

GaInNAs with bandgap 1.0 eV is a promising material for multi-junction solar cell applications. However, the poor quality of GaInNAs grown by metalorganic chemical vapor deposition hinders its device performance. Here to reap the benefits of 1.0-eV sub-cell, we focus on the optimization of annealing temperature and growth ambient of GaInNAs. The GaInNAs sub-cell exhibits a concentration reduction of shallow level defects when it is annealed at 700℃ for 20 min. As compared with the growth case using a hydrogen ambient, the N incorporation efficiency of GaInNAs can be enhanced during the growth in an N_2 ambient. Furthermore, background carbon concentration is observed to reduce in the as-grown GaInNAs epilayer. A GaInNAs sub-cell with 82% peak external quantum efficiency is obtained in a dual-junction GaInNAs/Ge solar cell. Finally, a monolithic Al Ga In P/Al Ga In As/Ga In As/GaInNAs/Ge five-junction solar cell is grown for space application. The fabricated device shows a conversion efficiency of 31.09% and a short-circuit current density of 11.81 m A/cm~2 under 1 sun AM 0 illumination.     

Anomalous Temperature Dependence of Photoluminescence in GaInNAs／GaAs Multiple Quantum Wells

Photoluminescence (PL) spectra of GaInNAs/GaAs multiple quantum wells grown on a GaAs substrate by molecular beam epitaxy are measured in a range of temperatures and excitation power densities.The energy position of the dominant PL peak shows an anomalous S-shape temperature dependence instead of the Varshni relation.By careful inspection,especially for the PL under lower excitation power density,two near bandedge peaks are well identified.These are assigned to carriers localized in nitrogen-induced bound states and interband excitonic recombinations,respectively.It is suggested that the temperature-induced switch of such two luminescence peaks in relative intensity causes a significant mechanism responsible for the S-shape shift observed in GaInNAs.A quantitative model based on the thermal depopulation of carriers is used to explain the temperature dependence of the PL peak related to N-induced bound states.     

Influences of quantum noises on direct-modulated properties of 1.3-μm InGaAsP/InP laser diodes

Due to the zero dispersion point at 1.3μm in optical fibres, 1.3-μm InGaAsP/InP laser diodes have become main light sources in fibre communication systems recently. Influences of quantum noises on direct-modulated properties of single-mode 1.3-μm InGaAsP/InP laser diodes are investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated single-mode laser system are calculated using the linear approximation method. We find that the stochastic resonance (SR) always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient between the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated InGaAsP/InP laser diodes and improve the quality of optical fibre communication systems.