Date of Award

Spring 1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Durgamadhab Misra

Second Advisor

Roy H. Cornely

Third Advisor

Kenneth Sohn

Fourth Advisor

N. M. Ravindra

Fifth Advisor

C. S. Wang

Abstract

This research thesis describes a new InxGa1-xAs/InAysP1-y/InP technology for long wavelength photodetectors and photodetector arrays. A unique and novel detector structure was designed and fabricated using Hydride Vapor Phase Epitaxy, for low leakage current photodetector arrays in the 1-2.6 µm wavelength region. Potential applications of InGaAs focal plane arrays include near-infrared spectroscopy, fluorescence, remote sensing, environmental sensing, space and astronomical applications. The unique design concepts included the step grading of InAsP layers, lower lattice mismatch between the two InAsP graded layers, lattice matched InAsP cap layer and InGaAs absorption layer, sulphur doping of InGaAs absorption layer and InAsP layers. Improved device fabrication techniques including rapid thermal annealing and precisely controlled diffusion were implemented during the processing of 1024 element linear photodetector arrays to reduce the dislocation density. An analysis of dark current, which is the critical parameter was required and is described in detail. The dark current analysis and the experimental results showed that the dark current is bulk dominated and is due to the crystal defects and dislocation density.

Each element of the focal plane array consisted of a 13 X 500 µm2 active area with an element to element spacing (pitch) of 25 µm The focal plane architecture designed had two 512 element (left and right) multiplexers and a 1024 element detector array and was integrated in a 24 pin dual-in-line package.

A unique and novel Si read-out multiplexer was designed and fabricated using radiation hardened N-well CMOS process. Each multiplexer unit cell consisted of a capacitive transimpedance amplifier, correlated double sampling circuit, threshold non uniformity correction circuit and an output buffer stage.

Integration and testing of InGaAs focal plane arrays with cut-off wavelengths of 1.7 µm, 2.2 µm and 2.6 µm are described. The performance of the focal plane arrays was analyzed in detail and the results showed that the 10 fA dark current levels could be achievable with 1024 element InGaAs/InP focal plane arrays in the 1-2.6 urn wavelength region. The dark current achieved from the test focal plane arrays was < I fA for 1.7 µm < 20 fA for 2.2 µm and < 50 fA for 2.6 µm cutoff wavelength. Radiation testing using proton, gamma and electron particle radiation on InGaAs photodetectors and photodetector arrays showed that InGaAs/InP focal plane arrays can with stand upto 15 Krad (Si) particle radiation. Comparison of the results achieved with published results of other technology (HgCdTe) operating at the same temperature shows that InGaAs/InP Focal Plane Arrays have lower dark current by a factor of 10-100.

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