气源分子束外延生长的InPBi薄膜材料中的深能级中心

利用深能级瞬态谱(DLTS)研究了气源分子束外延(GSMBE)生长的InP1-xBix材料中深能级中心的性质。在未有意掺杂的InP中测量到一个多数载流子深能级中心E1,E1的能级位置为Ec-0.38 e V,俘获截面为1.87×10~(-15)cm~2。在未有意掺杂的InP0.9751Bi0.0249中测量到一个少数载流子深能级中心H1,H1的能级位置为Ev+0.31 eV,俘获截面为2.87×10~(-17)cm~2。深中心E1应该起源于本征反位缺陷PIn,深中心H1可能来源于形成的Bi原子对或者更复杂的与Bi相关的团簇。明确这些缺陷的起源对于InPBi材料在器件应用方面具有重要的意义。     

The Self-Heating Effect of Quantum Cascade Lasers Based on a Spectroscopic Method

We investigate the self-heating effect of mid-infrared quantum cascade lasers by using a direct-based pulse injecting current and spectroscopy method. Based on the characterization system, the thermal characteristics of gas source MBE grown 8.4μm InP-based GalnAs/AIInAs DFB-QCLs are evaluated. The method and characterization system are also useful in evaluating the thermal characteristics of other types of mid-infrared diode lasers.     

InP-based InGaAs/InA1GaAs digital alloy quantum well laser structure at 2μm

The structural and optical characteristics of InP-based compressively strained InGaAs quantum wells have been significantly improved by using gas source molecular beam epitaxy grown InAs/Ino.53Ga0.47As digital alloy triangular well layers and tensile Ino.53Ga0.47As/InAiGaAs digital alloy barrier layers. The x-ray diffraction and transmission electron microscope characterisations indicate that the digital alloy structures present favourable lattice quality. Photo- luminescence （PL） and electroluminescence （EL） measurements show that the use of digital alloy barriers offers better optical characteristics than that of conventional random alloy barriers. A significantly improved PL signal of around 2.1μm at 300 K and an EL signal of around 1.95μm at 100 K have been obtained.     

Structural and Photoluminescence Properties for Highly Strain-Compensated InGaAs/InA1As Superlattice ＊

The effects of strain compensation are investigated by using twenty periods of highly strain-compensated InGaAs/InA1As superlattice. The lattice mismatches of individual layers are as high as about 1%, and the thicknesses are close to critical thicknesses. X-ray diffraction measurements show that lattice imperfectness is not serious but still present, though the structural parameters are within the range of theoretical design criteria for structural stability. Rough interfaces and composition fluctuations are the primary causes for lattice imperfecthess. Photoluminescence measurements show the large thermally activated nonradiative recombination in the sample. In addition, the recombination process gradually evolves from exeitonic recombination at lower temperatures to band-to-band recombination at higher temperatures, which should be considered in device applications.     

Low Threshold Distributed Feedback Quantum Cascade Lasers with Widely Spaced Emission Wavelengths

We report lasing properties of distributed feedback quantum cascade lasers （DFB QCLs） including a doublephonon-resonance active region, at wavelength of about 8.4 μm. A broad gain spectrum is generated due to the coupling between the lower laser level in the active region and the levels in the injector, and is demonstrated by the lasing spectrum of the corresponding Fabry-Perot QCLs whose width is 0.5 μm at 1.5 times of the threshold current. As a result, the DFB QCLs employing different grating periods exhibit a wavelength span of 0.18μm at room temperature and total wavelength coverage of 0.28μm at various heat sink temperatures. A high side mode suppression ratio of about 30dB and a low threshold current density of 1.78kA/cm^2 are achieved as the lasers operate at room temperature in pulsed mode.     

InP-based InGaAs/InAlGaAs digital alloy quantum well laser structure at 2 μm

The structural and optical characteristics of InP-based compressively strained InGaAs quantum wells have been significantly improved by using gas source molecular beam epitaxy grown InAs/In 0.53 Ga 0.47 As digital alloy triangular well layers and tensile In 0.53 Ga 0.47 As/InAlGaAs digital alloy barrier layers.The x-ray diffraction and transmission electron microscope characterisations indicate that the digital alloy structures present favourable lattice quality.Photoluminescence (PL) and electroluminescence (EL) measurements show that the use of digital alloy barriers offers better optical characteristics than that of conventional random alloy barriers.A significantly improved PL signal of around 2.1 μm at 300 K and an EL signal of around 1.95 μm at 100 K have been obtained.     

High-Temperature Operation of 8.5 μm Distributed Feedback Quantum Cascade Lasers

We present a distributed feedback quantum cascade laser （DFB-QCL） emitting at a wavelength of 8.5μm and operating up to 420K （147℃） with a low-threshold current density in pulsed mode. The DFB-QCLs studied are based on a four-well active design; the central portion of the waveguide consists of 60 periods of lattice matched InP-based InGaAs/AlInAs. In the design of the device, an active structure with lower doping and a deep-top grating process are utilized to achieve high temperature operation with a lower-threshold current density. At 420K, a low-threshold current density of 3.28 kA/cm^2 and a single mode peak power of 15mW are achieved on an epilayer-up mounting device with ridge width of 26μm and cavity length of 3.0mm. A side mode suppression ratio of 25 dB at 420 K is obtained.