C. E. Hurwitz

GaInAsP/InP avalanche photodiodes

Avalanche photodiodes for detection at 0.9–1.2 μm have been successfully fabricated in epitaxial layers of GaInAsP on InP substrates. Uniform avalanche gains in excess of 12, rise times of 150 psec or less, and low‐bias quantum efficiencies of 45% have been measured.

Ion‐implanted n‐ and p‐type layers in InP

InP has been doped by implantation with several different ions to yield layers of both n‐ and p‐type conductivity. Se+ and Si+ were found to be efficient n‐type dopants with activations in excess of 75% for moderate doses (1×1014 cm−2 at 400 keV). At doses of 1×1015 cm−2, sheet resistivities as low as 15 Ω/⧠ were obtained. Cd+, Mg+, and Be+ were all acceptors, with Mg+ yielding a sheet hole concentration as high as 5×1013 cm−2 for a dose of 1×1014 cm−2 at 150 keV. Reproducible annealing of implanted samples at temperatures up to 750 °C was accomplished with a pyrolytic phosphosilicate glass (PSG) encapsulation. Implants of Kr+ indicate that residual implantation damage is n type.

Silicon‐ and selenium‐ion‐implanted GaAs reproducibly annealed at temperatures up to 950 °C

A pyrolytic Si3N4 encapsulation technique has been used to permit reproducible annealing of implanted GaAs at temperatures as high as 950 °C. At low doses, electrical activity ≳70% has been achieved for both Si and Se. At high doses, sheet carrier concentrations and sheet resistivities of 1.8×1014/cm2 and 20 Ω/⧠, respectively, for Si and 7×1013/cm2 and 44 Ω/⧠, respectively, for Se have been measured.

Integrated GaAs-AlGaAs double-heterostructure lasers

Integrated structures consisting of a double‐heterostructure GaAs‐AlGaAs etched‐mesa Fabry‐Perot laser coupled to a high‐purity GaAs waveguide have been fabricated and tested. Room‐temperature threshold current densities as low as 7.5 kA/cm2 for 1‐μm‐thick active layers were measured.

Ionization coefficients of electrons and holes in InP

The ionization coefficients of electrons and holes in InP have been determined from photomultiplication measurements on abrupt‐junction low‐leakage np+ InP avalanche photodiodes. The ionization rate of holes ( β) was found to be greater than that for electrons (α), the ratio varying with peak electric field Em from β/α=3.8 at Em=4.85×105 V cm−1 to β/α=2.7 at Em=6.37×105 V cm−1.

Avalanche multiplication and noise characteristics of low‐dark‐current GaInAsP/InP avalanche photodetectors

High‐performance avalanche photodiodes responding out to 1.25 μm have been fabricated in inverted‐mesa n+‐InP/n‐GaInAsP/n‐InP/p+‐InP structures. Uniform avalanche gains of 700, dark current densities of 3×10−6 A/cm2 at M=10, and an excess‐noise factor of ∼3, also at M=10, have been measured. The low dark current results from the placement of the p‐n junction in the InP and from the use of a new passivation technique. Pulse‐response rise times, measured with an avalanche gain of 40 and limited by the rise time of the mode‐locked Nd:YAG laser pulse, were less than 160 psec.

HIGH POWER AND EFFICIENCY IN CdS ELECTRON BEAM PUMPED LASERS

Electron beam excitation of CdS crystals grown in an atmosphere of excess Cd has resulted in laser emission near 4900 A with 350 W of peak output power and 26.5% overall (35% internal) power efficiency at temperatures as high as 110°K. Laser action was observed, although at considerably reduced levels of power and efficiency, at temperatures up to 250°K. The high performance of the lasers appears to be due to increased crystal uniformity and to the introduction or enhancement of highly efficient radiative transitions, both of which result from the Cd‐rich growth conditions.

Diffusion length of moles in n‐InP

By measuring the photocurrent as a function of reverse bias for InP photodiodes with a range of junction depths, the hole diffusion length Lp of epitaxial n‐type InP (n∼1.5×1016 cm−3) was determined to be approximately 12 μm. This value of Lp is an order of magnitude larger than that determined by the electron beam induced current and surface photovoltage techniques. Reasons for these discrepancies, which involve geometrical and material considerations, respectively, are discussed.

INFRARED TRANSMISSION, MAGNETIC BIREFRINGENCE, AND FARADAY ROTATION IN EuO

Infrared transmission, magnetic birefringence, and Faraday rotation have been measured in single crystals of EuO as a function of temperature and magnetic field in the wavelength region between 1.5 and 20 μ. The most transparent samples have an absorption coefficient at 20°K less than 0.5 cm−1 in the range between 2.5 and 9 μ and less than 1.0 cm−1 at 10.6 μ. At 20°K and 9 kG the Faraday rotation varies from 660 deg/cm at 10.6 μ to 3 × 104 deg/cm at 2.5 μ and over 105 deg/cm at 1.5 μ.

High-Performance GalnAsP/InP Avalanche Photodetectors

High performance inverted-mesa GaInAsP/InP avalanche photodiodes responding out to 1.25 pm haye been fabricated. Uniform avalanche gains, M, of 700, dark current densities of 3 x 10-6 A/cm2 at M = 10, and an excess noise factor of -3 at M = 10 have been achieved by placing the p-n junction in the InP and using a new passivation technique. Pulse-response risetimes of less than 160 psec, limited by the risetime of the mode-locked Nd:YAG laser pulse, were measured with an avalanche gain of 40. Avalanche photodiodes (APDs) of the III-V quaternary alloy GaxIn1-xAsyP1-y on InP substrates have been under development in several laboratories for use in the 1.0-1.6 pm spectral region of interest for fiber optics applications. Typically, these devices, which have had the p-n junction located in the GaInAsP layer, have exhibited large values of dark current at biases sufficient to achieve gain, a condition that severely degrades the signal-to-noise performance and limits the gain to low values. Recently, however, Nishida et al. 1,2 have demonstrated in diffused structures that reductions in leakage current and increases in gain can be obtained by placing the p-n junction in the InP, so the high-field region is in the InP while the photogeneration region is in the GaInAsP. The noise performance of these devices was not discussed, but the low temperature (-190°C) noise characteristics of more conventional GaInAsP APDs were very recently published.3