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Photoconductor Liquid Crystal Display Cell Using Ion Implanted GaAs

IP.com Disclosure Number: IPCOM000086964D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Howard, WE: AUTHOR [+2]

Abstract

A fabrication technique is disclosed for making GaAs of high dark resistance so that it may be used in GaAs laser-addressed liquid crystal displays.

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Photoconductor Liquid Crystal Display Cell Using Ion Implanted GaAs

A fabrication technique is disclosed for making GaAs of high dark resistance so that it may be used in GaAs laser-addressed liquid crystal displays.

A sensitive display medium for laser beam-addressed displays can be made by combining a photoconductive (PC) layer with a liquid crystal (LC). A bias voltage is placed across the combination by means of transparent electrodes, and when the laser beam illuminates a spot on the PC, the voltage on the LC is increased and it switches to a scattering state. The PC/LC combination has been used in the past for enhancement of low intensity images (Beard, et al, Appl. Phys. Letters 22, 90, (1973)). A PC/ferroelectric combination has also been demonstrated for this purpose (Smith and Land, Appl. Phys. Letters 20, 169, (1972)).

For blue or green lasers, CdS appears to be a suitable PC, while for the He- Ne lasers, a mixture of CdS and CdSe may be suitable. For the important case of the GaAs injection laser (Lambda=0.8 to 0.85 Mu m), it is unlikely that a II-VI semiconductor with a sufficiently high dark resistance can be found (Rho>10/8/ Omega cm).

GaAs itself has the correct photoresponse and can be made in high resistivity form by Cr and oxygen doping (Blanc & Weisberg, Nature 192, 155, (1961) and Cronin & Haisty, J. Electrochem. Soc. 111, 874, (1964)). However, very critical control of the deposition conditions are required to produce a film of GaAs approximately 5mu m thick with sufficiently high resistivity (>10/8/ Omega cm).

Fabrication can be greatly simplified by producing the high resistivity by implantation of oxygen ions (Favennec, et al, Ion Implantation in Semiconductors & Other Materials, Plenum Press, p. 621). Any residual doping effects in the deposited film can easily be overcome by adjusting the oxygen dosage. The thickness of the film which can be compensated is limited to about 2.5 Mu m for a 3 MeV accelerator. However, since the absorption coefficient of GaAs is about 10/4/ cm/-1/ at 1.5 ev (0.85 Mu m), this thickness will absorb most of the incident light.

A typical PC/L...