Ultrahigh-Purity Undoped GaAs Epitaxial Layers Prepared by Liquid Phase Epitaxy

Abstract

A new automatic feedback potometer for physiological studies of water uptake by root systems is described. A dual-optical-fibre amplitude-modulating displacement transducer of improved sensitivity is employed to detect the changes in liquid level. The merits of optimal double-cut fibres, which make full use of the critical angle and improve coupling between the emitter and the receiver, have resulted in a sensor that is 64 times more responsive than the simple emitter-detector probe. Positioning the optical fibre transducer in a narrow capillary and using feedback to control the liquid level allows continuous measurement of volumes in the nanolitre range. The optical sensor used does not need re-calibration for the different salt solutions used in such studies.

Room Temperature Excitonic Electroabsorption Effect for High-Speed and Low-Driving Voltage Spatial Light Modulators

“…Finally, the sample was fixed on the glass coated with Au/Ge/Ni with a small window similar to back contact of the sample in order to transmit an incident light by using "Araldite" thermosetting epoxy resin. A GaAs epilayers are grown by LPE method which is similar to that reported elsewhere [5]. Prior to deposition Ohmic contact and spin coating of transparent Schottky contact, both surfaces of the sample were cleaned by solvent and rinsed with de-ionized (DI) water, and the removal of an oxidation layer by a diluted acid solution was preformed.…”

“…We have succeeded in growing ultrahigh purity GaAs layers by a liquid phase epitaxial method where residual impurity concentrations are of the order lower than 10 13 cm -3 and electron mobility are of the level of 200,000 cm 2 /Vs at 77K [5]. These epitaxial layers give large depletion width over 30 m at 0 V and show clear excitonic absorption peak at room temperature [6], resulting to highly efficient surface-normal modulators with a high contrast ratio of over 25 dB and the operating voltage of 32 V. However, the window diameter (300 m) is too wide to reach-through upto 26 V.…”

Low driving voltage spatial light modulator fabricated by ultrahigh-purity GaAs

“…In order to purify epilayers we used recyclic growth method [2]. Before fabricating device, epilayer was grown on semi-insulating (SI) GaAs substrate and the purity of Ga solution was measured by Hall measurement.…”

“…The epilayers were grown inside a quartz tube, utilizing a conventional sliding boat under a palladium-purified hydrogen carrier gas ambient [2]. GaAs epilayers with high mobility and low carrier concentration have low transmission loss and large depletion region because a sharp excition absorption can be observed even at room temperature.…”

Proposed Model of Electric Field Effects in High-Purity GaAs at Room Temperature

“…Surface normal mode results in low extinction ratio due to short depletion width. We succeeded in growing high-purity epitaxial layers (~1 × 10 13 cm −3 ) and obtaining high extinction ratio over 20 dB [1]. Based on the well known model [2] [3] (Franz-Keldysh effect) such large extinction ratio cannot be explained.…”