Az Li

Properties of gas source molecular beam epitaxy grown wavelength extended InGaAs photodetector structures on a linear graded InAlAs buffer

The properties of gas source molecular beam epitaxy grown wavelength extended (2.4 µm) InGaAs photodetector structures on a linear graded InAlAs buffer with different grading rates have been investigated by means of XRD and PL techniques in conjunction with optical and atomic force microscopy. Results show that full relaxation and favorable optical characteristics of the active layers only occur for the wafers with a mismatch grading rate of about 1.2% µm−1 or lower, whereas moderate morphology and structural quality could be achieved for a mismatch grading rate up to 2.4% µm−1. A thin GSMBE grown linear graded InAlAs buffer layer of 1.4 µm is sufficient to relax the strain of an InGaAs layer with 1.7% mismatch to the InP substrate and reach a good quality of the wafer. The relaxation mechanisms of the buffer at different grading rates were also discussed.

InP-based InAs/InGaAs quantum wells with type-I emission beyond 3 μm

This work reports on InAs/In0.53Ga0.47As strain compensated quantum well structures on InP-based metamorphic buffer to generate the type-I emission of beyond 3 μm. The metamorphic buffer is composed of InxAl1−xAs graded layer and In0.8Ga0.2As virtual substrate layer. Atomic force microscope, transmission electron microscope and x-ray diffraction measurements show the moderate surface and structural properties. A photoluminescence signal up to 3.05 μm has been achieved at 300 K, which is one of the longest wavelengths from the interband emission of InP-based antimony-free structure. It is promising to employ this quantum well structure on metamorphic buffer for the laser demonstration with emission around 3 μm.

Molecular beam epitaxial growth, characterization and performance of high-detectivity GaInAsSb/GaSb PIN detectors operating at 2.0 to 2.6 μm

Abstract Molecular beam epitaxy has been employed to grow Ga x In 1− x As 1− y Sb y PIN detectors operating at 2.0 to 2.6 μm on (100)-oriented GaSb substrates. The epitaxial layers were characterized by X-ray double-crystal diffraction, Fourier transform infrared spectroscopy, electron microprobe analysis, and Hall effect measurements. The background hole concentration and mobility at room temperature are (4–5) × 10 16 cm −3 , 254 cm 2 /V·s and 9 × 10 15 cm −3 , 970 cm 2 /V·s for GaInAsSb and GaSb, respectively. For a PIN mesa front-illuminated photodetector, a maximum external quantum efficiency of 65% without anti-reflection coating and a peak detectivity D λ ∗ at 2.5 μm of 3.0 × 10 9 cm Hz 1/2 / W with a cut-off wavelength of 2.6 μm at room temperature have been achieved.

Fourier transform infrared spectroscopy approach for measurements of photoluminescence and electroluminescence in mid-infrared

An improved Fourier transform infrared spectroscopy approach adapting to photoluminescence and electroluminescence measurements in mid-infrared has been developed, in which diode-pumped solid-state excitation lasers were adopted for photoluminescence excitation. In this approach, three different Fourier transform infrared modes of rapid scan, double modulation, and step scan were software switchable without changing the hardware or connections. The advantages and limitations of each mode were analyzed in detail. Using this approach a group of III-V and II-VI samples from near-infrared extending to mid-infrared with photoluminescence intensities in a wider range have been characterized at room temperature to demonstrate the validity and overall performances of the system. The weaker electroluminescence of quantum cascade lasers in mid-infrared band was also surveyed at different resolutions. Results show that for samples with relatively strong photoluminescence or electroluminescence out off the background, rapid scan mode is the most preferable. For weaker photoluminescence or electroluminescence overlapped with background, double modulation is the most effective mode. To get a better signal noise ratio when weaker photoluminescence or electroluminescence signal has been observed in double modulation mode, switching to step scan mode should be an advisable option despite the long data acquiring time and limited resolution.

Current self-oscillation and driving-frequency dependence of negative-effective-mass diodes

We have analyzed spatio-temporal current patterns and current–voltage characteristics of negative-effective-mass (NEM) p+pp+ diodes driven by dc bias and terahertz (THz) electromagnetic radiation. Interesting nonlinear dynamics are presented, including current synchronization, frequency doubling, and transition to chaos. Discussions of suppressing possible chaos in NEM semiconductor devices are included.

Comparison of thermal characteristics of antimonide and phosphide MQW lasers

The thermal characteristics of antimonide ridge waveguide MQW lasers have been investigated numerically and experimentally, and compared with phosphide lasers in detail. Using the finite-element method, the heat accumulation and dissipation process of the lasers under CW and pulse driving conditions have been simulated, and quantitative thermal time constants were introduced to describe the cooling efficiency of the lasers. The non-uniform temperature distribution inside the active core of the laser and its effects on lasing spectra have been discussed, and confirmed by the measurement of the broadening of the lasing spectrum towards the blue side. A way to improve the thermal property of antimonide lasers have also been proposed and discussed.

Spectrum dynamics of negative-effective-mass oscillators under terahertz radiation

We report on a theoretical investigation of power spectrum dynamics in negative-effective-mass (NEM) p+pp+ oscillators under the influence of terahertz (THz) electromagnetic radiation. Possible types of transport states (periodic or chaotic) and transitions between them are examined with the intensity and frequency of the radiation as controlling parameters. When the driving frequency is fixed to the self-oscillating frequency times the inverse Golden ratio, the resulting power spectrum pattern displays a very complex mosaic scenario with a self-similar emergence of high-order mixing frequencies.

Photoluminescence studies of InAs/InGaAs/AlAs strained single quantum well structures

We report on steady‐state photoluminescence spectra from a strained InAs/In0.53Ga0.47As/AlAs single quantum well (SQW) structure grown by molecular beam epitaxy. Strong luminescence in the wavelength of ∼1.9 μm for the well width of 7 ML was obtained. The radiative process in the InAs quantum well is dominated by the excitonic luminescence. Based on a steadystate of the lumines‐ cence intensity allow us to conclude that the photogenerated carriers in the well come from tunneling from the InGaAs layer via the AlAs barrier.

Difference of luminescent properties between strained InAsP/InP and strain-compensated InAsP/InGaAsP MQWs

Abstract Strained InAs 0.43 P 0.57 /InP and strain-compensated InAs 0.43 P 0.57 /In 0.7 Ga 0.3 As 0.43 P 0.57 multiple quantum well (MQW) structures were grown by gas source molecular beam epitaxy. The observations of up to 5 satellite-diffraction peaks from the high-resolution X-ray diffraction measurements demonstrate good crystalline quality for both structures. The temperature dependence of the 1e–1hh transition energies, the line width of photoluminescence (PL) spectra and emission efficiency η of the two quantum well structures are compared by low-temperature PL measurements. The temperature dependence of the 1e–1hh transitions of the two quantum well structures is similar to that of InAs 0.43 P 0.57 bulk material. The thermal activation energies obtained for strain-compensated MQW are larger than those obtained for the strained one. Consequently, the PL emission efficiency decays much slower for the strain-compensated MQW than that for the strained one when temperature increases, indicating the superior temperature stability of luminescent efficiency for the strain-compensated MQW. The obtained results can be used as references to the design and fabrication of optoelectronic devices.

Parametric study on lattice-matched and pseudomorphic InGaAs/InAlAs/InP modulation-doped heterostructures grown by GSMBE

Abstract Modulation-doped In x Ga 1 − x As/In y Al 1 − y As/InP heterostructures have been grown with a diffusion pumped V80H gas source molecular beam epitaxy system. Their electrical properties have been studied with Hall measurements. The effects of spacer layer thickness and buffer layer structure (InAlAs or InAlAs + InP) on lattice-matched and pseudomorphic In x Ga 1 − x As/In y Al 1 − y As/InP 2DEGs and HEMTs characteristics have been investigated in detail. Crystalline and interface qualities can be improved by adding an InP buffer layer before the InAlAs buffer, resulting in an improvement in material electrical properties. A thicker spacer layer will cause a decrease of electron gas density and an increase of electron mobility. Adopting strained channel and Schottky layers can dramatically improve material electrical performance. For InGaAs/InAlAs/InP pseudomorphic 2DEG (P-2DEG) structures, electron mobilities of 11 230 cm 2 /V · s at n s of 2.3 × 10 12 cm −2 at 300 K and 6.52 × 10 4 cm 2 /V · s at n s of 2.1 × 10 12 cm −2 at 77 K were obtained and μ of 9273 cm 2 /V · s at 3.6 × 10 12 cm −2 and 4.5 × 10 4 cm 2 /V · s at n s of 3.1 × 10 12 cm −2 for both strained InGaAs channel layers and InAlAs Schottky layers in P-HEMT structures were achieved.