R. Sidhu

A long-wavelength photodiode on InP using lattice-matched GaInAs-GaAsSb type-II quantum wells

We report a photodiode on InP substrate with a cutoff wavelength of 2.39 /spl mu/m and peak room-temperature external quantum efficiency of 43% at 2.23 /spl mu/m. Type-II GaInAs-GaAsSb quantum wells lattice-matched to InP were placed in the absorption region for long wavelength absorption. The device showed a peak detectivity of 5.6/spl times/10/sup 10/ cm/spl radic/HzW/sup -1/ at 200 K.

Low-noise avalanche photodiodes with graded impact-ionization-engineered multiplication region

A novel impact-ionization-engineered multiplication region for avalanche photodiodes is reported. By pseudograding the multiplication region with materials of different ionization threshold energies, the impact ionization of the injected carrier type is localized, while that of the feedback carrier type is suppressed. Low noise (k/sub eff/<0.1), low dark current, and high gain were achieved.

InGaAs/InAlAs avalanche photodiode with undepleted absorber

We report an avalanche photodiode with an undepleted p-type InGaAs absorption region and a thin InAlAs multiplication layer. The motivation for utilizing an undepleted absorption layer, which is similar to that in the unitraveling carrier photodiode, is to reduce the dark current. A dark current below 1 nA at a gain of 10 and a gain–bandwidth product of 160 GHz are demonstrated.

Low-noise impact-ionization-engineered avalanche photodiodes grown on InP substrates

We report low noise multiplication region structures designed for avalanche photodiodes grown on InP substrates. By either implementing a single heterostructure or using a pseudograded structure in the multiplication region, better control of spatial distribution of impact-ionization for both injected and feedback carriers can be achieved; localization of the carrier impact ionization process has resulted in very low excess noise.

GaAsSb: a novel material for near infrared photodetectors on GaAs substrates

We have studied the molecular beam epitaxy (MBE) growth of GaAsSb on GaAs substrates. The optical properties and composition of GaAsSb layer strongly depend on the growth temperature, the Ga growth rate, and the As and Sb fluxes and their ratios. We also report on two GaAsSb-GaAs photodiode structures operating at 1.3 /spl mu/m. The peak quantum efficiency was 54% for the GaAsSb resonant-cavity-enhanced (RCE) p-i-n photodiode and 36% for the RCE GaAsSb avalanche photodiode (APD) with separate absorption, charge, and multiplication regions (SACM). At 90% of the breakdown, the dark current of the SACM APD was 5 nA. The GaAsSb SACM APD also exhibited very low multiplication noise and k/sub eff/ was approximately 0.1, which is the lowest ever reported for APDs operating at 1.3 /spl mu/m.

High Power Photodiode Wafer Bonded to Si Using Au With Improved Responsivity and Output Power

High power photodiodes wafer bonded to Si using a gold intermediate layer were demonstrated. A fabricated 20-mum-diameter photodiode exhibited a bandwidth of ~18 GHz, a large-signal saturation-current of ~50 mA, and a peak responsivity of ~1 A/W. Both the responsivity and the saturation current of the Au-bonded photodiode were improved compared to the photodiode with the same structure on InP substrate

Diffusion mechanisms of indium and nitrogen during the annealing of InGaAs quantum wells with GaNAs barriers and GaAs spacer layers

In this article, we discuss two indium diffusion mechanisms that are present during the rapid thermal annealing of InxGa1−xAs quantum wells (x=0.18, 0.22, and 0.26) with GaNyAs1−y barriers (y=0.6 or 1.2%). Samples were grown with and without a GaAs spacer layer in between the quantum well and barrier. The dominant mechanism is dependent on the amount of thermal energy applied during the annealing process. At low annealing times and temperatures, we have observed that In-Ga intra-diffusion entirely within the quantum well is dominant. For the higher times and temperatures, In-Ga inter-diffusion between the quantum well and barrier becomes dominant. These observations were confirmed by high-resolution x-ray diffraction and the peak emission wavelengths were measured by room-temperature photoluminescence. We have also observed that nitrogen had diffused from the GaNAs barriers into the InGaAs quantum wells in all of our annealed samples. In addition, the commonly observed indium-content dependent diffusion i...

Photodetectors: UV to IR

This paper surveys recent work in several photodetector areas including high-speed, low-noise avalanche photodiodes, solar-blind ultra-violet PIN photodiodes, and quantum dot infrared photodetectors (QDIPs).

Atomic force microscopy study of sapphire surfaces annealed with a H2O flux from a baffled molecular-beam epitaxy effusion cell loaded with Al(OH)3

We present an atomic force microscopy (AFM) study of sapphire surfaces that contain scratches with various severities. The objective was to observe the effects of substrate annealing at 850°C for 200min with a H2O-based overpressure resulting from an Al(OH)3 powder that was thermally cracked at 1200°C. The Al(OH)3 was decomposed into Al2O3 and H2O according to a partial Bayer process in a modified molecular-beam epitaxy (MBE) effusion cell, which was equipped with homemade baffles placed at its outlet. These homemade, simple-to-construct tantalum baffles allow for the selective outfluxing of gaseous species, from those that are solid based. A UTI™ 100C-model mass spectrometer was used to monitor the species present at the sapphire surface during annealing. Any aluminum-based solid species from the Al(OH)3 were not observed in the mass spectrum, although the H2O-based species were. The sapphire substrates were annealed in a Varian Gen II™ MBE system, with H2O beam equivalent pressures (BEPs) of 5×10−6 and ...

Inert gas maintenance for molecular-beam epitaxy systems

Molecular-beam epitaxy (MBE) most often involves the use of highly toxic and combustible materials, which may subject maintenance personnel to increased health risks. In our efforts to reduce these hazards, we describe the use of inert gas maintenance equipment and procedures that can be employed during the opening of MBE growth chambers. Our operations involve the use of nitrogen-purged glovebags that are sealed over the open port of the growth chamber, wherein applicable tasks are performed through appropriate gloveports of the glovebag. We also describe the associated equipment utilized inside of the glovebags, which aid in the removal of the substrate manipulator and effusion cells. The benefits of reducing the exposure of air to the growth chamber are observed after a bakeout of 145h, wherein the AsO partial pressure within the growth chamber was a factor of 10 lower due to our inert gas maintenance procedures than without. The use of these glovebags allows us to both terminate our bakeout approximat...