C. Jelen

Growth and characterization of InGaAs/InGaP quantum dots for midinfrared photoconductive detector

We report InGaAs quantum dot intersubband infrared photodetectors grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The optimum growth conditions were studied to obtain uniform InGaAs quantum dots constructed in an InGaP matrix. Normal incidence photoconductivity was observed at a peak wavelength of 5.5 μm with a high responsivity of 130 mA/W and a detectivity of 4.74×107 cm H1/2/W at 77 K.

Gas-source molecular beam epitaxy growth of an 8.5 μm quantum cascade laser

We demonstrate preliminary results for an 8.5 μm laser emission from quantum cascade lasers grown in a single step by gas-source molecular beam epitaxy. 70 mW peak power per two facets is recorded for all devices tested at 79 K with 1 μs pulses at 200 Hz. For a 3 mm cavity length, lasing persists up to 270 K with a T0 of 180 K.

Noise performance of InGaAs-InP quantum-well infrared photodetectors

Dark current noise measurements were carried out between 10 and 10/sup 4/ Hz at T=80 K on two InGaAs-InP quantum-well infrared photodetectors (QWIPs) designed for 8-/spl mu/m infrared (IR) detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependant gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate (/spl sim/7/spl times/10/sup 22/ cm/sup -3//spl middot/s/sup -1/) is similar to AlGaAs-GaAs QWIPs with similar peak wavelengths, but the gain is 50/spl times/ larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers.

Aluminum free GaInP/GaAs quantum well infrared photodetectors for long wavelength detection

We demonstrate quantum well infrared photodetectors based on a GaAs/Ga0.51In0.49P superlattice structure grown by gas-source molecular beam epitaxy. Wafers were grown with varying well widths. Wells of 40, 65, and 75 A resulted in peak detection wavelengths of 10.4, 12.8, and 13.3 μm with a cutoff wavelength of 13.5, 15, and 15.5 μm, respectively. The measured peak and cutoff wavelengths match those predicted by eight band theoretical analysis. Measured dark currents were lower than equivalent GaAs/AlGaAs samples.

Low-threshold and high power λ∼9.0 μm quantum cascade lasers operating at room temperature

We report a low threshold current density and high power for λ∼9 μmAlInAs/GaInAs quantum cascade lasers operating at room temperature. The threshold current density is 1.95 kA/cm2 at 300 K and 0.61 kA/cm2 at 80 K for 5 μs pulses at 200 Hz repetition rate. The peak output power is 700 mW at room temperature and 1.3 W at 80 K per two facets for cavity length is 3 mm with a stripe width of 20 μm. The characteristic temperature T0 is 185 °C. The slope efficiency is 450 and 800 mW/A at 300 and 80 K, respectively. In continuous wave operation, the output power is more than 150 mW at 80 K and 25 mW at 140 K. This high performance was achieved by improving the material growth and processing technology.

High detectivity GaInAs-InP quantum-well infrared photodetectors grown on Si substrates

In this letter, we report an improvement in the growth and the device performance of GaInAs-InP quantum well infrared photodetectors grown on Si substrates. Material growth techniques, like low-temperature nucleation layers and thick buffer layers were used to grow InP on Si. An in situ thermal cycle annealing technique was used to reduce the threading dislocation density in the InP-on-Si. Detector dark current was reduced 2 orders of magnitude by this method. Record high detectivity of 2.3 /spl times/ 10/sup 9/ cmHz/sup 1/2//W was obtained for QWIP-on-Si detectors in the 7-9 /spl mu/m range at 77 K.

InGaAlAs-InP quantum-well infrared photodetectors for 8-20-/spl mu/m wavelengths

We demonstrate the first long-wavelength quantum-well infrared photodetectors using the lattice-matched n-doped InGaAlAs-InP materials system. Samples with AlAs mole fractions of 0.0, 0.1, and 0.15 result in cutoff wavelengths of 8.5, 13.3, and 19.4 /spl mu/m, respectively, a 45/spl deg/ facet coupled illumination responsivity of R=0.37 /spl mu/m and detectivity of D/sub /spl lambda//*=3/spl times/10/sup 8/ cm/spl middot//spl radic/(Hz)/spl middot/ at T=77 K, for a cutoff wavelength /spl lambda//sub c/=13.3 /spl mu/m have been achieved. Based on the measured intersubband photoresponse wavelength, a null conduction band offset is expected for In/sub 0.52/Ga/sub 0.21/Al/sub 0.27/As-InP heterojunctions.

Solar-blind AlxGa1-xN p-i-n photodetectors grown on LEO and non-LEO GaN

There is currently a strong interest in developing solid- state, UV photodetectors for a variety of applications. Some of these are early missile threat warning, covet space to space communications, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The III-Nitride material system is an excellent candidate for such applications due to its wide, reagent detection. The III-Nitride material system is an excellent candidate for such applications due to its wide, direct bandgaps and robust material nature. However, despite many inherent material advantages, the III-Nitride material system typically suffers from a large number of extended defects which degrade material quality and device performance. One technique aimed at reducing defect densities in these materials is lateral epitaxial overgrowth (LEO). In this work, we present a preliminary comparison between AlGaN UV, solar-blind p-i-n photodiodes fabricated form LEO GaN and non-LEO GaN. Improvements in both responsivity and rejection ratio are observed, however, further device improvements are necessary. For these, we focus on the optimization of the p- i-n structure and a reduction in contact resistivity to p- GaN and p-AlGaN layers. By improving the structure of the device, GaN p-i-n photodiodes were fabricated and demonstrate 86 percent internal quantum efficiency at 362 nm and a peak to visible rejection ratio of 105. Contact treatments have reduced the contact resistivity to p-GaN and p-AlGaN by over one order of magnitude form our previous results.

Characterization of high quality GaInP/GaAs superlattices grown on GaAs and Si substrates by gas source molecular beam epitaxy

We report an analysis of the heteroepitaxial interfaces in high quality GaInP–GaAs superlattices grown simultaneously on GaAs and Si substrates by gas source molecular beam epitaxy. These two superlattices have been studied using high resolution x‐ray diffraction measurements. Sharp superlattice satellites, with very little broadening, are observed within a 6° range for the sample on GaAs. Photoluminescence peaks with full widths at half‐maximums of 5 and 7 meV are obtained at 4 K for samples with 58 A wells on GaAs and Si, respectively. Room temperature exciton absorption is observed in the photovoltage measurements for a superlattice grown on Si substrate. The thicknesses determined by x‐ray analysis are consistent with those obtained by a Kronig–Penny model fitting of the photovoltage spectroscopy.

High-responsivity GaInAs/InP quantum well infrared photodetectors grown by low-pressure metalorganic chemical vapor deposition

We have studied the dependence of the well doping density in n-type GaInAs/InP quantum well IR photodetectors (QWIPs) grown by low-pressure metalorganic chemical vapor deposition. Three identical GaInAs/InP QWIP structures were grown with well sheet carrier densities of 1 by 1011 cm-2, 3 by 1011 cm-2, and 10 by 1011 cm-2; all three samples had very sharp spectral response at (lambda) equals 9.0 micrometers . We find that there is a large sensitivity of responsivity, dark current, noise current, and detectivity with the well doping density. Measurements revealed that the lowest-doped samples had an extremely low responsivity relative to the doping concentration while the highest-doped sample had an excessively high dark current relative to doping. The middle-doped sample yielded the optimal results. This QWIP had a responsivity of 33.2 A/W and operated with a detectivity of 3.5 by 1010 cmHz1/2W-1 at a bias of 0.75 V and temperature of 80 K. This responsivity is the highest value reported for any QWIP in the (lambda) equals 8-9 micrometers range. Analysis is also presented explaining the dependence of the measured QWIP parameters to well doping density.