R. Kiefer

Room-temperature low-threshold low-loss continuous-wave operation of 2.26 μm GaInAsSb/AlGaAsSb quantum-well laser diodes

Strained single- and triple-quantum-well (SQW and TQW), large optical cavity GaInAsSb/AlGaAsSb/GaSb laser diodes emitting at 2.26 μm are investigated. Internal loss coefficients as low as 5 and 7.7 cm−1 for the SQW and TQW, respectively, and relatively high internal quantum efficiencies of 65% (SQW) and 69% (TQW) were obtained. Extrapolated threshold current densities for infinite cavity lengths of 55 and 150 A/cm2 have been deduced for the SQW and TQW, respectively. These values scale very well with the number of QWs and are among the lowest reported for diode lasers in this wavelength range. A differential quantum efficiency as high as 50% and a total power efficiency of 23% were achieved at 280 K. The temperature dependence of the threshold current density revealed a high characteristic temperature of 110 K. Single-ended output powers of 240 mW in continuous-wave mode and exceeding 0.5 W in pulsed operation were obtained for a TQW laser with high-reflection/antireflection coated facets at 280 K, mounte...

Light-emitting diodes and laser diodes based on a Ga1−xInxAs/GaAs1−ySby type II superlattice on InP substrate

We report on the fabrication and characterization of light-emitting diodes (LEDs) and laser diodes with a staggered type II Ga1−xInxAs/GaAs1−ySby superlattice (SL) as the active region. SLs were grown strain compensated on the InP substrate using metalorganic chemical vapor deposition. The LEDs show room-temperature electroluminescence up to 2.14 μm, the index-guided diode lasers displayed cw laser emission at 1.71 μm up to 300 K. The spontaneous emission spectrum was found to show a significant blueshift with increasing injection current density, resulting in shorter laser emission wavelengths for the diode laser than for the LED.

Optoelectronic properties of photodiodes for the mid-and far-infrared based on the InAs/GaSb/AlSb materials family

The optoelectronic properties of short-period InAs/(GaIn)Sb superlattices (SLs) grown by molecular beam epitaxy on GaSb substrates are discussed. We report on the optimization of the SL materials properties with special emphasis on the use for infrared detection devices. The materials quality is evaluated by using high resolution x-ray diffraction, atomic force microscopy, and photoluminescence spectroscopy. In- plane magneto-transport investigations were performed applying mobility spectrum analysis. The SL diodes were analyzed performing standard electro-optical measurements. The observation of resonances in the I-V curves in the regime of Zener-tunneling due to Wannier-Stark localization opens a new tool for the electrical investigation of photodiodes with low band gap energy. The status of the processing technology is reported demonstrating the feasibility for the fabrication of 256 X 256 focal plane arrays operating in the 8-to-12 micrometers atmospheric window. In addition, results are given for mid-infrared SL-diodes, grown with lattice matched AlGaAsSb barriers instead in the binary InAs/GaSb SL system.

Comprehensive modeling of the electro-optical-thermal behavior of (AlGaIn)(AsSb)-based 2.0 μm diode lasers

Strained triple-quantum-well, large-optical-cavity GaInSb/AlGaAsSb/GaSb diode lasers emitting at 1.98 μm at 300 K are investigated with regard to their high-power capability. As the heating of the active region is a limiting factor for these devices, a quantitative model is derived to simulate the performance of these lasers including thermal effects. The standard laser parameters, deduced from measurements on ridge waveguide lasers, and the measured thermal resistance of the mounted devices were then taken as input parameters. The output power and power efficiency of the lasers calculated using the presented model. Good agreement was found between calculated data and the measurements for different heatsink temperatures as well as for different laser geometries and mounting techniques. The maximum output power achieved for p-side down mounted 1000×150 μm2 broad-area laser was 1.7 W at 300 K in cw operation.

A coplanar X-band AlGaN/GaN power amplifier MMIC on s.i. SiC substrate

This work presents a two-stage high-power amplifier monolithic microwave integrated circuit (MMIC) operating between 9 GHz and 11 GHz based on a fully integrated AlGaN/GaN high electron mobility transistor (HEMT) technology on s.i. SiC substrate and is suitable for radar applications. The MMIC device with a chip size of 4.5/spl times/3 mm/sup 2/ yields a linear gain of 20 dB and a maximum pulsed saturated output power of 13.4 W at 10 GHz equivalent to 3.3 W/mm at V/sub DS/=35V, 10% duty cycle, and a gain compression level of 5 dB. Further, dc reliability data are given for the MMIC HEMT technology.

20W GaN HPAs for Next Generation X-Band T/R-Modules

High power amplifiers for a next generation of T/R-modules for future X-band active array antennas are realized on the bases of novel AlGaN/GaN HEMT structures, which are epitaxially grown on SiC wafer substrates. Both, hybrid and monolithically integrated circuits are designed and realized as key elements for transmit chains. Based on hybrid designs excellent peak power levels of 23 W (43.6 dBm) with an associated power added efficiency (PAE) of 29% are realized. Over a bandwidth of 2 GHz (X-band) the output power levels are above 20 W. In a more sophisticated approach first monolithically integrated circuits (MMICs) are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 20 W (43 dBm) with an associated PAE of 30% are measured on small size 12 mm2 chips. Highest ever reported maximum power added efficiency values of up to 36.5% are achieved

Improvement of λ≈5 μm quantum cascade lasers by blocking barriers in the active regions

We report the improvement of quantum cascade lasers emitting at λ∼5 μm by introducing AlAs blocking barriers together with strain-compensating InAs layers into the active regions. The blocking barriers are designed to selectively prevent electrons in the initial laser state from tunneling out of the active region, while maintaining the high tunneling probabilities of the electrons in the final laser states. Adopting blocking barriers, the maximum peak power per facet at 77 K (300 K) is increased from 285 (30 mW) to 900 mW (240 mW), and the maximum operation temperature in pulsed mode has been improved from 320 to 350 K with respect to a reference sample without blocking barriers.

GaN MMIC based T/R-Module Front-End for X-Band Applications

Amplifiers for a next generation of T/R-modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the bases of novel AlGaN/GaN HEMT structures. Both, low noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high power amplifier (HPA) are measured. The measured noise figure of the low noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multilayer LTCC technology.

Comprehensive analysis of the internal losses in 2.0μm (AlGaIn)(AsSb) quantum-well diode lasers

We have fabricated and characterized high-power 2.0 μm-wavelength (AlGaIn)(AsSb) quantum-well diode lasers emitting a power of 1.7 W in continuous-wave operation and over 9 W in pulsed operation at 300 K heat sink temperature. For potential further improvement of laser performance, the different contribution to the internal losses αi has been analyzed in detail for the present laser structure. Consistent results have been obtained for a series of samples, for which different design parameters were varied systematically: As expected, the losses in the cladding layers are dominated by free carrier absorption in the p-doped cladding. The cross section for free-hole absorption in Al0.84Ga0.16As0.06Sb0.94 is determined to σP=4.6×10−17 cm2, which is comparable to values reported in the literature for (AlGaIn)(AsP)-based lasers emitting at 1.5 μm. The losses in the active region were found to increase linearly with increasing number of quantum wells at a rate of 1.5 cm−1 per quantum well, whereas the losses in t...

Large signal modeling of AlGaN/GaN HEMTs with P/sub sat/>4 W/mm at 30 GHz suitable for broadband power applications

Large signal modeling and investigations of an AlGaN/GaN HEMT processed on SiC with l/sub g/=150 nm are performed with respect to broadband amplifiers up to 30 GHz. Output power values of 3.4 W or 4.25 W/mm at 18 GHz and P/sub out/=1.6 W, equivalent to 4 W/mm at 30 GHz, are measured. The device modeling shows good agreement of the measured and modeled power sweeps at 10 GHz and 30 GHz. The large signal simulations show the suitability of AlGaN/GaN HEMTs for multi-band amplifiers in the K-band.