Q.K Yang

The effect of dispersion of the refractive index on the performance of mid-infrared quantum cascade lasers

In this paper, we present the results of the calculation and design for waveguide and the dependence on the performance of mid-infrared InAlAs/InGaAs/InP quantum cascade (QC) lasers grown by gas source molecular beam epitaxy. The dispersion of refractive indices are calculated by taking into account the contribution of the free-carrier concentration absorption. We also report the first GSMBE grown InAlAs/InGaAs/InP QC lasers emitting at 5.1mm, operated in pulse mode up to 130 K with T0 of 208 K and J0 of 2.6 kA/cm 2 . For the QC laser designed with lower waveguide cladding InP concentration of 1 � 10 18 cm � 3 , it does not lase. Presented theoretical and experimental results indicate that the free-carrier absorption in both upper InGaAs contact layer and lower InP waveguide cladding does play an important role in the dispersion of the index of refraction of semiconductors at mid–far-infrared wavelengths and influence the performance of QC lasers. # 2001 Elsevier Science B.V. All rights reserved.

Growth and characterization of high-quality GaInAs/AlInAs triple wells

The growth and characterization of GaInAs/AlInAs triple quantum well structures are reported. The structures are characterized with high-resolution X-ray diffraction combined with high-resolution simulation based on the dynamical theory of X-ray diffraction and with photoluminescence. The good agreement in both peak position and intensity of the high-resolution X-ray diffraction spectra with the high-resolution simulation reveals the precise control of the epilayer thickness and the good quality of interfaces. The photoluminescence spectra are analyzed concerning the peak position, interface roughness, and lineshape. These three aspects correlate well with each other, and the interface roughness is determined by fluctuations of 1 monolayer occurring every 3 effective exciton radii in the lateral plane.

GSMBE grown infrared quantum cascade laser structures

In this paper we show the evaluated results of a quantum cascade laser (QCL) structure with a vertical transition and a Bragg reflector grown by gas source molecular beam epitaxy (GSMBE). The Al 0.48 In 0.52 As/Ga 0.47 In 0.53 As QCL structures lattice matched to the InP substrate consists of alternating 25 periods of undoped coupled-quantum-well active regions with compositionally graded layers, a superlattice graded region to provide strong electron confinement in the upper state using a Bragg reflector and an InP buffer layer. The laser operates in the temperature range from 8 to 250 K with measured integrated optical powers up to 70 mW at 8 K, and 5 mW at 250 K. The high-resolution emission spectrum of the laser at 250 K provides direct evidence of laser action from the narrowing of the strong line and clearly illustrating the longitudinal mode structure.

Characterization of GaN grown by RF plasma MBE

Abstract GaN (Gallium nitride) has been grown successfully on sapphire by RF plasma MBE through optimizing the growth condition. Two dimensional triple axis mapping (TDTAM) was used to characterize the GaN epilayers. The dislocation density in the epilayers was estimated to be about 7.8×108 cm−2 according to the mosaic model. The 77K photoluminescence (PL) of the Si-doped GaN with different concentration show that Si can act both donor and acceptor at very high concentration. Transmission spectrum has also been measured for further understanding of the sample.

GSMBE grown In0.49Ga0.51P/(In)GaAs/GaAs high hole mobility transistor structures

In this paper, we report novel In 0.49 Ga 0.51 P/(In)GaAs/GaAs high-hole mobility transistor structures with different p-channel and doping methods. Electrical and optical properties of the grown structures were investigated by Van der Pauw Hall measurement and low-temperature photoluminescence. The current-voltage characteristics were performed on field effect transistors with T-shaped gates. By using delta-doping technique, 2DHG densities of 2.78 ×10 12 and 1.02 x 10 12 cm - 2 with mobility of 191 and 2831 cm 2 /V s at 300 and 77 K for In 0.49 Ga 0.51 P/GaAs structures have been achieved. For In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs structures, 2DHG densities increased to 2.84×10 12 and 1.29 ×10 12 cm -2 with mobility increasing to 208 and 2972 cm 2 /V s at 300 and 77 K, respectively. Photoluminescence spectra of In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs modulation doped heterostructure shows a peak located at 1.310 eV, which is attributed to a transition from V 3/2 band to conduction band. The processed high-hole mobility transistors have a maximum extrinsic transconductance of 35mS/mm and a maximum saturation current of 57mA/mm at 300 K.

Detection of lead ions with AlGaAs/InGaAs pseudomorphic high electron mobility transistor

Lead poisoning is a serious environmental concern, which is a health threat. Existing technologies always have some drawbacks, which restrict their application ranges, such as real time monitoring. To solve this problem, glutathione was functionalized on the Au-coated gate area of the pseudomorphic high electron mobility transistor (pHEMT) to detect trace amounts of Pb2+. The positive charge of lead ions will cause a positive potential on the Au gate of the pHEMT sensor, which will increase the current between the source and the drain. The response range for Pb2+ detection has been determined in the concentrations from 0.1 pmol/L to 10 pmol/L. To our knowledge, this is currently the best result for detecting lead ions.

Coupling coefficients for guided modes in distributed feedback quantum cascade lasers

Abstract In this paper, we have calculated the coupling coefficients for guided modes in distributed feedback quantum cascade lasers based on the perturbation theory. The coupling coefficients are given as functions of the grating depth g with g ranging from 0 to 400 nm. When the grating depth is about 250 nm the typical coupling coefficient for quantum cascade lasers working at 5–13 μm is ∼30 cm −1 .