Daniel Yap

Electrooptical Characterization of MWIR InAsSb Detectors

InAs1−xSbx material with an alloy composition of the absorber layer adjusted to achieve 200-K cutoff wavelengths in the 5-μm range has been grown. Compound-barrier (CB) detectors were fabricated and tested for optical response, and Jdark–Vd measurements were taken as a function of temperature. Based on absorption coefficient information in the literature and spectral response measurements of the midwave infrared (MWIR) nCBn detectors, an absorption coefficient formula α(Ε, x, T) is proposed. Since the presently suggested absorption coefficient is based on limited data, additional measurements of material and detectors with different x values and as a function of temperature should refine the absorption coefficient, providing more accurate parametrization. Material electronic structures were computed using a k·p formalism. From the band structure, dark-current density (Jdark) as a function of bias (Vd) and temperature (T) was calculated and matched to Jdark–Vd curves at fixed T and Jdark–T curves at constant Vd. There is a good match between simulation and data over a wide range of bias, but discrepancies that are not presently understood exist near zero bias.

GaAs and silica-based integrated optical time-shift network for phased arrays

We compare the GaAs and Silica-based approaches for realizing integrated time-shift networks. The performance of a fully functional 2-cm X 2-cm monolithic GaAs circuit is reviewed in detail. In addition, we describe the design of an optoelectronic- switched network that uses Silica-based star-couplers and waveguide arrays.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

ARPA analog optoelectronic module program: packaging challenges for analog optoelectronic arrays

This paper describes the packaging challenges associated with array-based transmitters and receivers used for analog fiber-optic links. The optoelectronic modules are being developed under an ARPA Analog Optoelectronic Module TRP. The paper will focus on the development of optoelectronic array modules using silicon waferboard technology for application to personal communication systems.

GaAs optical time-shift network for steering a dual-band microwave phased-array antenna

A monolithic optical time-shift network is described which is designed to steer a dual-band microwave phased array antenna at 2 and 10 GHz. The advantages of using cascade type network architectures to achieve the desired resolution are demonstrated. The implementation of different delay times in this optical time-shifter via bias control of detectors integrated monolithically on a GaAs wafer is described.

Integrated optoelectronic circuits with InP-based HBTs

Integrated optoelectronic circuits that are capable of very high speeds or high functionality have been demonstrated using InP-based heterojunction bipolar transistors (HBTs). Optoelectronic receivers contain photodetectors fabricated from the same epitaxial material structure as the HBTs. High-functionality digital receivers, analog receiver arrays as well as analog-to-digital converters have been realized. Optoelectronic modulation circuits for signal transmission also contain separately grown, surface-coupled multiple- quantum-well (MQW) modulators.

MWIR InAs 1-x Sb x nCBn detectors data and analysis

In InAs1-xSbx material alloy composition was adjusted to achieve 200K cutoff wavelengths in the 5 μm range. Reflectance was minimized and absorption in the InAs1-xSbx material maximized by the use of pyramid shaped structures fabricated in the InAs1-xSbx material which function as an AR coating. Compound-barrier (CB) detectors were fabricated and tested for optical response and dark current density versus bias measurements were acquired as a function of temperature. For 5 μm cutoff detectors, QE is high, ~ 75 % between 4.0 μm and 4.6 μm and > 80 % between 2.0 μand 4.0 μm, demonstrating the efficacy of the pyramids as photon trap structures and as a replacement for multi-layer AR-coatings. Jdark in the low 10-3 A/cm2 range at 200 K and low 10-5 A/cm2 range at 150 K was measured at the bias at which the QE peaked.

rf optoelectronic transmitter and receiver arrays on silicon wafer boards

Silicon waferboard technology based on etched and deposited passive-alignment features has been applied to the fabrication of optoelectronic transmitter and receiver arrays for rf applications. Using silicon waferboards, we have aligned both 1 by 4 buried-heterostructure laser arrays and 1 by 4 PIN photodetector arrays to optical fiber ribbons. Besides serving as mechanical carriers and alignment guides, the silicon wafers can also be used as rf or microwave substrates. We introduce rf-optoelectronic receiver arrays based on such enhanced silicon waferboards.

Operating characteristics of InGaAs-GaAs MQW hetero-nipi waveguide modulators

We report frequency response measurements of optical MQW nipi waveguide modulators, observing a -3-dB bandwidth as high as 110 MHz. These devices have only 900-/spl Aring/-thick intrinsic regions, and thus can achieve very high fields with modest reverse bias voltages. We also measured absorption modulation (32 dB) and a phase change figure of merit as low as V/sub /spl pi///spl times/L=0.8 V mm at a detuning of 115 meV below the photoluminescence peak. We compare ion-implanted selective contacts with traditional selective metal contacts.<<ETX>>

Fabrication of high-operating temperature (HOT), visible to MWIR, nCBn photon-trap detector arrays

We describe our recent efforts in developing visible to mid-wave (0.5 µm to 5.0 µm) broadband photon-trap InAsSb-based infrared detectors grown on GaAs substrates operating at high temperature (150-200K) with low dark current and high quantum efficiency. Utilizing an InAsSb absorber on GaAs substrates instead of an HgCdTe absorber will enable low-cost fabrication of large-format, high operating temperature focal plane arrays. We have utilized a novel detector design based-on pyramidal photon trapping InAsSb structures in conjunction with compound barrier-based device architecture to suppress both G-R dark current, as well as diffusion current through absorber volume reduction. Our optical simulation show that our engineered pyramid structures minimize the surface reflection compared to conventional diode structures acting as a broadband anti-reflective coating (AR). In addition, it exhibits > 70-80% absorption over the entire 0.5 µm to 5.0 µm spectral range while providing up to 3× reduction in absorber volume. Lattice-mismatched InAs0.82Sb0.18 with 5.25 µm cutoff at 200K was grown on GaAs substrates. 128×128/60μm and 1024×1024/18μm detector arrays that consist of bulk absorber as well as photon-trap pyramid structures were fabricated to compare the detector performance. The measured dark current density for the diodes with the pyramidal absorber was 3× lower that for the conventional diode with the bulk absorber, which is consistent with the volume reduction due to the creation of the pyramidal absorber topology. We have achieved high D* (< 1.0 x 1010 cm √Hz/W) and maintain very high (< 80 %) internal quantum efficiency over the entire band 0.5 to 5 µm spectral band at 200K.

InAsSb detectors for visible to MWIR high-operating temperature applications

The Photon-Trap Structures for Quantum Advanced Detectors (PT-SQUAD) program requires MWIR detectors at 200 K. One of the ambitious requirements is to obtain high (> 80 %) quantum efficiency over the visible to MWIR spectral range while maintaining high D* (> 1.0 x 1011 cm √Hz/W) in the MWIR. A prime method to accomplish the goals is by reducing dark diffusion current in the detector via reducing the volume fill ratio (VFR) of the detector while optimizing absorption. Electromagnetic simulations show that an innovative architecture using pyramids as photon trapping structures provide a photon trapping mechanism by refractive-index-matching at the tapered air/semiconductor interface, thus minimizing the reflection and maximizing absorption to > 90 % over the entire visible to MWIR spectral range. InAsSb with bandgap appropriate to obtaining a cutoff wavelength ~ 4.3 μm is chosen as the absorber layer. An added benefit of reducing VFR using pyramids is that no AR-coating is required. Compound-barrier (CB) detector test structures with alloy composition of the InAsSb absorber layer adjusted to achieve 200 K cutoff wavelength of 4.3 μm (InAsSb lattice-matched to GaSb). Dark current density at 200 K is in the low 10-4 A/cm2 at Vd = -1.0 V. External QE ~ 0.65 has been measured for detectors with a Si carrier wafer attached. Since illumination is through the Si carrier wafer that has a reflectance of ~ 30 %, this results in an internal QE > 0.9.