Michael J. Lange

Thin-film organic position sensitive detectors

One-dimensional 3-cm-long organic heterojunction position sensitive detectors (OPSDs) have been fabricated with an optical beam spatial resolution of 20 /spl mu/m. The device relies on a current divider in a uniformly resistive indium-tin-oxide detector anode layer to determine beam position. This architecture makes the position measurement insensitive to fluctuations in incident light beam intensity and background illumination. The response of the OPSD shows high linearity, low positional error, and high spatial resolution. The device functions over a wide range of incident beam powers from 10 /spl mu/W to >1 mW, and is capable of continuously tracking optical beams, with a tracking velocity exceeding 2 m/s.

A three wavelength infrared focal plane array detector element

We have demonstrated a novel three wavelength InGaAs focal plane array pixel element for detection at wavelengths from 0.9-2.6 /spl mu/m, where each of three wavelength sensitive detectors are individually addressable. This device consists of successively smaller bandgap layers of In/sub x/Ga/sub 1/spl minus/x/As (x/spl ges/0.53), separated by compositionally graded layers of InAs/sub y/P/sub 1/spl minus/y/ to decrease defects induced by lattice mismatch strain with the InP substrate. The various layers were selectively removed so that p-n junctions with different wavelength response are formed. The three detectors have quantum efficiencies between 55 and 95% for front illumination and 15 and 60% for back illumination, and dark currents from 0.01 to 10 mA/cm/sup 2/.<<ETX>>

In/sub 0.53/Ga/sub 0.47/As/InP floating guard ring avalanche photodiodes fabricated by double diffusion

In/sub 0.53/Ga/sub 0.47/As/InP separate absorption and multiplication region avalanche photodiodes (SAM-APDs) with doubly diffused floating guard rings have been demonstrated. The planar, front-side illuminated devices are easily fabricated and incorporate strong guarding against edge and surface breakdown. Edge gain is suppressed both by the action of the floating guard rings and by the grading of the p-n junction at the outer edges of the active region that results from the second diffusion. Uniform gains as high as 85 have been measured at multiplied dark currents <100 nA. Multiplied dark currents below 5 nA have been measured at 90% of breakdown, with capacitances below 400 fF for front-side illuminated devices. The low values of dark current and capacitance, as well as the ease of fabrication, make the devices well suited for fiber-optic applications.<<ETX>>

InGaAs/InP focal plane arrays for visible light imaging

We report on recent results in using InGaAs/InP focal plane arrays for visible light imaging. We have fabricated substrate-removed backside illuminated InGaAs/InP focal plane arrays down to a 10 μm pitch with high quantum efficiency from 0.4 μm through 1.7 μm. This focal plane array can be used for visible imaging as well as imaging eye-safe lasers. Using the InGaAs/InP materials system for visible imaging applications has several advantages over silicon based CMOS or CCD imagers including inherent radiation hardness, the ability to simultaneously achieve low crosstalk (less than 1%), and bandwidths exceeding 1 GHz, as well as the ability to image out to 1.7 μm.

A monolithically integrated 1 x 4 switchable photodiode array with preamplifier for programmable frequency filters and optical interconnects

An InGaAs-InP 1/spl times/4 p-i-n photodiode array has been monolithically integrated with switching junction field-effect transistors and a transimpedance preamplifier. The switching on-off ratio at the output of the preamplifier is 60 dB. As an optical receiver, the circuit has a 3-dB bandwidth of 1.1 GHz and a sensitivity of -25 dBm at 1 Gb/s, BER=10/sup -9/, and 1.55-/spl mu/m wavelength. A programmable frequency filter has been demonstrated as an application of this novel circuit.

Study of InxGa1−xAs/InAsyP1−y structures lattice mismatched to InP substrates

Material properties of several lattice‐mismatched InxGa1−xAs/InAsyP1−y (0.66<x<0.84, 0.29<y<0.66) alloys grown on InP substrates are investigated. The lattice constants and compositions were measured using x‐ray diffraction and electron probe microanalysis. Photoluminescence, white light transmission, and detector cutoff wavelengths were used to determine the band gap of InxGa1−xAs as a function of In concentration x. The three methods agree to within 3%. The quality of the grown layers was also investigated using these techniques, in addition to cross‐section transmission electron microscopy and Nomarsky optical microscopy. The dependence of the experimental measurements of band gap and lattice constant on material composition, measured by electron probe microanalysis, was compared against theoretical values.

Avalanche gain in InAs y P/sub 1-y/ (0.1<y<0.3) photodetectors

Uniform avalanche gains of 40 to 80 are observed in InAs/sub y/P/sub 1-y/ (0.1<y<0.3) grown on p-type InP substrates, with lattice strains as high as 1%. These devices have a primary dark current as low as 200 pA, with the dark current increasing, in some cases, to only 1 nA at 90% of the breakdown voltage. The ionization coefficients for both electrons and holes are approximately equal, and the generation of secondary carriers is primarily via ionization of defect levels. The InAs/sub yx/P/sub 1-y/ layers have the same lattice parameter as compositions of In/sub x/Ga/sub 1-x/ which absorb light wavelengths /spl les/2.1 /spl mu/m, suggesting that this material combination has potential for use in avalanche photodiodes that detect moisture in LIDAR and gas-sensing applications in the mid-IR spectral range.<<ETX>>

Room temperature 640x512 pixel near-infrared InGaAs focal plane array

We report on the performance of a 640 X 512 pixel, indium gallium arsenide (In53Ga47As) focal plane array (FPA). The device has 25 micrometer pixels and represents the largest and finest pitched imager demonstrated in this material system. The device is sensitive to the 0.9 micrometer-to-1.7 micrometer short wave infrared band and features a room temperature detectivity, D*, greater than 5 X 1012 cm- (root)Hz/W with greater than 98% of the pixels operable. The performance of the In53Ga47As photodiode array is such that at room temperature the focal plane array is read noise- limited. The presentation will include a description of the FPA fabrication and assembly as well as characterization of dark current versus temperature, spectral response, and resolution. The implications of these results to applications such as passive night vision imaging, active illumination, covert surveillance, target designation using eye safe lasers, and target acquisition and tracking will be discussed.

Reduction of 1/f noise in multiplexed linear In/sub 0.53/Ga/sub 0.47/As detector arrays via epitaxial doping

A significant (2-5*) reduction in 1/f noise was observed in In/sub 0.53/Ga/sub 0.47/As photodetector arrays read out by a PMOS multiplexer, when the epitaxial InP cap layer doping was changed from undoped to sulfur-doped n type of about 3*10/sup 16/ cm/sup -3/. A further decrease was observed when the InP buffer layer was also changed from undoped to sulfur-doped n type of about 5*10/sup 17/ cm/sup -3/. Data was presented for the variation of 1/f noise, within a temperature range of 18 degrees C to -40 degrees C. Surface states at the InP cap/SiN interface appears to be the primary source of 1/f noise, with the bulk states at the n/sup -/In/sub 0.53/Ga/sub 0.47/As buffer hetero-interface as a secondary source. Increased n-type doping in the high-bandgap InP cap and buffer layers may reduce electron trapping, and thus 1/f noise. The measured noise spectrum of InGaAs photodetectors varies as f/sup y/ with y being approximately -0.45 for device structures with doped and undoped InP can layers. For a doped InP buffer layer, this value of y is -0.3. >

128x128 InGaAs detector array for 1.0-1.7 μm

A two-dimensional 128 x 128 detector array for the 1.0 - 1.7 micron spectral region has been demonstrated with indium gallium arsenide. The 30 micron square pixels had 60 micron spacing in both directions and were designed to be compatible with a 2D Reticon multiplexer. Dark currents below 100 pA, capacitance near 0.1 pF, and quantum efficiencies above 80 percent were measured. Probe maps of dark current and quantum efficiency are presented along with pixel dropout data and wafer yield which was as high as 99.89 percent (7 dropouts) in an area of 6528 pixels and 99.37 percent (103 dropouts) over an entire 128 x 128 pixel region.