With optimized buffer design, we demonstrate a new InAs/AlSb resonant tunneling diode (RTD) on lattice-unmatched semi-insulating (SI) GaAs (100) substrates aiming for terahertz oscillators. To obtain high crystal quality and smooth surface, 5 periods InGaAs/GaAs (2ML/2ML) superlattices (SLs) buffer layer was used as dislocation filters (DFs). Xray diffraction (XRD) measurement showed the full width at half maximum (FWHM) of 331arcsec and surface roughness of 2.4nm over 10μm×10μm. 8-μm-diam diodes were fabricated by standard mesa process. I-V characteristic of the diodes shows negative conductivity at room temperature and a peak current density of 1.79×105A • cm-2 was achieved.
In this work, we report a separate absorption and multiplication avalanche photodiode (SAM-APD) with 100% cut-off wavelength of ~2.1 μm at 300 K grown by molecular beam epitaxy. The electron-dominated avalanche mechanism multiplication region was designed as a multi-quantum well structure consisting of AlAsSb/GaSb H-structure superlattice and Al0.3In0.7AsSb digital alloy. At room temperature, the device exhibits a maximum multiplication gain of 79 under -13.3 bias voltage.
A two terminal short wavelength infrared heterojunction phototransistors based on type-II InAs/AlSb/GaSb on GaSb substrate are designed fabricated and presented. With the base thickness of 40 nm, the device exhibited 100% cut-off wavelengths of ~2.3 μm at 300K. The saturated peak responsivity value is of 325.5 A/W at 300K, under front-side illumination without any anti-reflection coating. A saturated optical gain at 300K was 215 a saturated dark current shot noise limited specific detectivity of 4.9×1011 cm·Hz1/2/W at 300 K was measured. Similar heterojunction phototransistor structure was grown and fabricated with different method of processing for high speed testing. For 80μm diameter circular diode size under 20 V applied reverse bias, a -3 dB cut-off frequency of 1.0 GHz was achieved, which showed the potential of type-II superlattice based heterojunction phototransistors to be used for high speed detection.
Frequency combs, spectra of phase-coherent equidistant lines, have revolutionized time and frequency metrology. The recently developed quantum cascade laser (QCL) comb has exhibits great potential with high power and broadband spectrum. However, in the terahertz (THz) range, cryogenic cooling has to be applied for THz QCL combs. We report a room temperature THz frequency comb at 3.0 THz based on difference-frequency generation from a mid-IR QCL comb. A largely detuned distributed-feedback grating is integrated into the QCL cavity to provide the single mode operation as well as enhanced spatial hole-burning effect for multimode comb operation. Multiheterodyne spectroscopy with multiple equally spaced lines by beating it with a reference Fabry-Pérot comb confirms the THz comb operation. This type of THz comb provides a new solution to chip-based high-speed high-resolution THz spectroscopy with compact size at room temperature.
Third generation of infrared imagers demand performances for higher detectivity, higher operating temperature, higher resolution, and multi-color detection all accomplished with better yield and lower manufacturing costs. Antimonide-based gap-engineered Type-II superlattices (T2SLs) material system is considered as a potential alternative for Mercury- Cadmium-Telluride (HgCdTe) technology in all different infrared detection regimes from short to very long wavelengths for the third generation of infrared imagers. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. We will present the most recent research results on Antimonide-based gap-engineered Type-II superlattices, such as high-performance dual-band SWIR/MWIR photo-detectors and focal plane arrays for different infrared regimes, toward the third generation of infrared imaging systems at the Center for Quantum Devices. Comparing metal-organic chemical vapor deposition (MOCVD), vs molecular beam epitaxy (MBE).
We present the recent development of high performance compact frequency comb sources based on mid-infrared quantum cascade lasers. Significant performance improvements of our frequency combs with respect to the continuous wave power output, spectral bandwidth, and beatnote linewidth are achieved by systematic optimization of the device's active region, group velocity dispersion, and waveguide design. To date, we have demonstrated the most efficient, high power frequency comb operation from a free-running room temperature continuous wave (RT CW) dispersion engineered QCL atλ ~5-9μm. In terms of bandwidth, the comb covered a broad spectral range of 120 cm-1 with a radio-frequency intermode beatnote spectral linewidth of 40 Hz and a total power output of 880 mW at 8 μm and 1 W at λ~5.0μm. The developing characteristics show the potential for fast detection of various gas molecules. Furthermore, THz comb sources based on difference frequency generation in a mid-IR QCL combs could be potentially developed.
Mid-infrared lasers, emitting in the spectral region of 3-12 μm that contain strong characteristic vibrational transitions of many important molecules, are highly desirable for spectroscopy sensing applications. High efficiency quantum cascade lasers have been demonstrated with up to watt-level output power in the mid-infrared region. However, the wide wavelength tuning, which is critical for spectroscopy applications, is still largely relying on incorporating external gratings, which have stability issues. Here, we demonstrate the development a monolithic, widely tunable quantum cascade laser source emitting between 6.1 and 9.2 μm through an on-chip integration of a sampled grating distributed feedback tunable laser array with a beam combiner. A compact tunable laser system was built to drive the individual lasers within the array and coordinate the driving of the laser array to produce desired wavelength. A broadband spectral measurement (520cm-1) of methane shows excellent agreement with Fourier transform infrared spectrometer measurement. Further optimizations have led to high performance monolithic tunable QCLs with up to 65 mW output while delivering fundamental mode outputs.
We present recent progress on the development of monolithic, broadband, widely tunable midinfrared quantum cascade lasers. First, we show a broadband midinfrared laser gain realized by a heterogeneous quantum cascade laser based on a strain balanced composite well design of Al0.63In0.37As/Ga0.35In0.65As/Ga0.47In0.53As. Single mode emission between 5.9 and 10.9 μm under pulsed mode operation was realized from a distributed feedback laser array, which exhibited a flat current threshold across the spectral range. Using the broadband wafer, a monolithic tuning between 6.2 and 9.1 μm was demonstrated from a beam combined sampled grating distributed feedback laser array. The tunable laser was utilized for a fast sensing of methane under pulsed operation. Transmission spectra were obtained without any moving parts, which showed excellent agreement to a standard measurement made by a Fourier transform infrared spectrometer.
We demonstrate GaAs-based metamorphic lasers in the 1.3-1.55 μm telecom range grown by molecular beam epitaxy.
The introduction of dopants in a compositionally graded layer is shown to significantly influence material properties, as
well as having impact on the laser device design. Investigating and understanding of strain relaxation and dislocation
dynamics is useful for improving material quality, performance and robustness of metamorphic devices. We demonstrate
pulsed lasing up to 1.58 μm and continuous wave lasing at 1.3 μm at room temperature with low threshold currents.
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