Takahiro Isshiki

High-saturation-current charge-compensated InGaAs-InP uni-traveling-carrier photodiode

Charge compensation is utilized in an InGaAs-InP uni-traveling-carrier photodiode to mitigate the space-charge effect. A 20-/spl mu/m-diameter photodiode achieved a bandwidth of 25 GHz and large-signal 1-dB compression current greater than 90 mA; the output power at 20 GHz was 20 dBm. A smaller /spl sim/100-/spl mu/m/sup 2/ photodiode exhibited a bandwidth of 50 GHz and large-signal 1-dB compression current greater than 50 mA. The maximum RF output power at 40 GHz was 17 dBm.

Origin of dark counts in In0.53Ga0.47As∕In0.52Al0.48As avalanche photodiodes operated in Geiger mode

A dark count rate in InP-based single photon counting avalanche photodiodes is a limiting factor to their efficacy. The temperature dependence of the dark count rate was studied to understand its origin in In0.53Ga0.47As∕In0.52Al0.48As separate-absorption-charge-multiplication avalanche photodiodes. The dark count rate was observed to be a very weak function of temperature in the range from 77Kto300K. Various mechanisms for dark count generation were considered. Simulations of band-to-band tunneling in the In0.52Al0.48As multiplication layer were found to agree well with the experimental temperature dependence of dark count rate at various excess biases. To reduce tunneling-induced dark counts, a suitable design change to the detector structure is proposed.

Geiger mode operation of an In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode

Low-temperature photon counting with gated mode quenching is demonstrated with separate absorption, charge, and multiplication avalanche photodiodes that have an In/sub 0.52/Al/sub 0.48/As multiplication layer. A minimum of ten dark counts per second and single-photon detection efficiency of 16% were achieved at 130 K.

Single photon counting Geiger mode InGaAs(P)/InP avalanche photodiode arrays for 3D imaging

We have designed, fabricated and characterized InGaAs/InP Geiger-mode avalanche photodiode (APD) 32 x 32 arrays optimized for operation at both 1.06 and 1.55 μm wavelengths Single element devices with a thick multiplication layer thickness showed dark count rate as low as 60 kHz at a 3 V overbias, while photon detection efficiencies at a wavelength of 1.55 μm exceed 30% at 2 V overbias. Back illuminated 32 x 32 detector arrays exhibited breakdown uniformity of greater than 97% and excellent dark current uniformity. Detector arrays were integrated with low-noise read-out integrated circuits for an imaging demonstration. 3D imaging was demonstrated using 1.06 micron detector arrays.

Monolithic multi-cell GaAs laser power converter with very high current density

A very high current density 2-Volt Laser Power Photovoltaic GaAs converter has been fabricated to produce over 360 mW of output power with monochromatic illumination of one optical Watt at 810 nm. To build-up the voltage, the converter consists of two interconnected N/P GaAs elements integrated in series on the semi-insulating GaAs substrate. Several technological issues, including, conductive losses through the sheet for the series interconnection of elements, have been successfully addressed. This device operates at a nominal optical power density of 57W/cm/sup 2/, which is equivalent to over 700 suns of AM1.5D illumination, demonstrating feasibility of fabricating high voltage integrated cells for concentrator applications.

High-saturation-current charge-compensated InGaAs/InP uni-traveling-carrier photodiode

In this paper a high-saturation-current charge-compensated InGaAs/InP uni-traveling-carrier photodiode with charge compensated collector layer is demonstrated. A 16 /spl mu/m diameter photodiode has demonstrated an output current of 80 mA and a bandwidth of 30 GHz.

Multijunction solar cells with subcell materials highly lattice-mismatched to germanium

The performance of a series of metamorphic GaInP and GaInAs solar cells grown on Ge with lattice-mismatch ranging from 0% to 2.4% is reported, with emphasis on device structures with 0.5% and 1.6% mismatch. Dual-junction cells with moderately lattice-mismatched (0.2% and 0.5%) structures have already reached electrical performance comparable to lattice-matched devices, at about 26% efficiency under AM0, 1-sun condition. Development efforts to date on highly lattice-mismatched (1.6% mismatch) structures have resulted in 22.6% efficiency dual-junction cells, with many improvements still possible. Spectral response measurements reveal excellent quantum efficiency (QE) for metamorphic GaInP and GaInAs materials, with a measured internal QE of over 90%. The offsets between the bandgap voltage (E/sub g//q) and the open-circuit voltage (V/sub OC/) of GaInP and GaInAs metamorphic cells were kept below 550 mV and 450 mV, respectively. Experimental results indicate that lattice-mismatched GalnP/GalnAs dual-junction cells can achieve higher energy conversion efficiency than lattice-matched GaInP/GaInAs dual-junction solar cells.

High-power charge-compensated unitraveling-carrier balanced photodetector

Balanced photodetectors with top-illuminated charge-compensated unitraveling-carrier photodiodes designed for high-power applications are demonstrated. A 20-/spl mu/m-diameter photodiode balanced pair achieved a bandwidth of 10 GHz, and a large-signal saturation current of 25 mA for each photodiode. A 10-/spl mu/m-diameter photodiode balanced pair achieved a bandwidth of 26 GHz, and a large-signal saturation current of 15 mA for each photodiode. Broad-band common mode rejection ratio and noise suppression were also characterized.

Performance of very low dark current SWIR PIN arrays

Boeing Spectrolab has grown, fabricated and tested InGaAs PIN arrays with less than 1 nA/cm2 dark current density at 280 °K. The PIN diodes display greater than 1 A/W responsivity at -100 mV reverse bias with about 50 fF of diode capacitance.

High-performance InP Geiger-mode SWIR avalanche photodiodes

LAser Detection And Ranging (LADAR) is a promising tool for precise 3D-imaging, which enables field surveillance and target identification under low-light-level conditions in many military applications. For the time resolution and sensitivity requirements of LADAR applications, InGaAsP/InP Geiger-mode (GM) avalanche photodiodes (APDs) excel in the spectrum band between 1.0~1.6 μm. Previously MIT Lincoln Laboratory has demonstrated 3D LADAR imaging in the visible and near infrared (1.06 μm) wavelengths with InP/InGaAsP GM-APD arrays. In order to relieve the design tradeoffs among dark count rate (DCR), photo detection efficiency (PDE), afterpulsing, and operating temperature, it is essential to reduce the DCR while maintaining a high PDE. In this paper we will report the progress of GM-APD detectors and arrays with low DCR and high PDE at 1.06 μm. In order to improve both DCR and PDE, we optimized the multiplication layer thickness, substrate, and epitaxial growth quality. With an optimized InP multiplier thickness, a DCR as low as 100 kHz has been demonstrated at 4V overbias at 300 °C. and at 240 K, less than 1 kHz DCR is measured. A nearly 40% PDE can be achieved at a DCR of 10 kHz at the reduced temperature.