Resonant cavity infrared detectors (RCIDs) can reduce the noise in sensing a laser signal by strongly suppressing background photocurrent at wavelengths outside the narrow spectral band of interest. We recently reported an RCID with 100-nm-thick InAsSb/InAs absorber, GaAs/AlGaAs bottom mirror, and Ge/SiO2 top mirror. At T = 300 K, the external quantum efficiency reached 58% atλres ≈ 4.6 μm, with linewidth δλ = 27 nm. The characteristics at 125 K implied a specific detectivity of 5.5 × 1012 cm Hz½/W, which is more than 3× higher than for a state-of-the-art broadband HgCdTe device operating at that temperature. However, a prominent variation with mesa diameter of the deposited Ge spacer thickness made it difficult to predictably control λres for devices processed with a given diameter. This has been addressed by measuring the reflectivity spectrum following deposition of the spacer, so that thicknesses of the top mirror’s SiO2 and Ge layers could be adjusted appropriately to attain a targeted resonance. This was especially beneficial in matching the λres for a small mesa, needed to minimize the capacitance in high-frequency measurements, to the emission wavelength of a given ewquantum cascade laser.
Over the last two years, our group has reported the first room-temperature continuous-wave (RTCW) fixed wavelength VCSELs operating above 3 microns, in both optically pumped and electrically pumped devices. Our optically pumped 3.3um devices employ one or two wafer-bonded GaAs/AlGaAs mirrors, in conjunction with a type I InGaAsSb/AlInGaAsSb quantum well active region. Our electrically pumped 3.3um devices employ a bottom waferbonded GaAs/AlGaAs mirror, top deposited ZnSe/ThF4 mirror, and type II interband cascade (ICL) active region. These fixed wavelength devices lay a foundation for tunable devices in the spectrally rich 3-5um region. Narrowly tunable devices can use thermal tuning, by variation of pump power (optically pumped devices), bias current (electrically pumped devices), or device temperature (both electrically and optically pumped devices). In this paper, we describe tunable CW optically pumped devices with >4nm of tuning near 3.3um using variation of pump power. CW electrically pumped devices show ~2nm tuning near 3.3um using variation of bias current. These results are a critical first step towards an inexpensive and high-speed methane sensing source. A first generation of MEMS-tunable optically pumped devices has achieved 70nm tuning range near 3.34um.
Millimeter-wave (mmW)/sub-mmW/THz region of the electro-magnetic spectrum enables imaging thru clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Therefore considerable interest exists in developing low cost millimeter-wave imaging (MMWI) systems. Previous MMWI systems have evolved from crude mechanically scanned, single element receiver systems into very complex multiple receiver camera systems. Initial systems required many expensive mmW integrated-circuit low-noise amplifiers. In order to reduce the cost and complexity of the existing systems, attempts have been made to develop new mmW imaging sensors employing direct detection arrays. In this paper, we report on Raytheon’s recent development of a unique focal plane array technology, which operates broadly from the mmW through the sub-mmW/THz region. Raytheon’s innovative nano-antenna based detector enables low cost production of 2D staring mmW focal plane arrays (mmW FPA), which not only have equivalent sensitivity and performance to existing MMWI systems, but require no mechanical scanning.
Improved LWIR sensors are needed for defense applications. We report an advance in sensor
technology based on diodes in type-II strained layer superlattice structures built in the
InAs/GaSb/AlSb materials system. A key feature of the devices is a pair of complementary barriers,
namely, an electron barrier and a hole barrier formed at different depths in the growth sequence. The
structure is known as CBIRD. This work is a collaborative effort between Raytheon Vision Systems
and Jet Propulsion Laboratory, with design and growth being performed at JPL, and processing and
testing at RVS. We have analyzed the current-voltage characteristics as functions of temperature and
junction area, and have measured the spectral response and quantum efficiency as functions of bias
voltage. From the temperature dependence of the dark current in a typical case, we infer that the
effective barrier height is 0.175 eV. This indicates that dark current is limited by the barriers rather
than diffusion or GR mechanisms occurring within the absorber region where the bandgap is 0.13 eV.
The barriers prove to be very effective in suppressing the dark current. In the case of a detector
having a cutoff wavelength of 9.24 μm, we find R0A > 105 ohm cm2 at 78 K, as compared with about
100 ohm cm2 for an InAs/GaSb homojunction of the same cutoff. For good photo response, the
device must be biased to typically -200 or -250 mV. In this condition we find the internal quantum
efficiency to be greater than 50%, while the RA remains above 104 ohm cm2. Thus, the device shows
both high RA and good quantum efficiency at the same operating bias. We have also measured the
capacitance of the CBIRD device as functions of bias and frequency to help characterize the behavior
of the barriers. A 256×256 focal plane array was fabricated with this structure which showed at 78K a
responsivity operability of more than 99%.
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