P. W. Foy

JUNCTION LASERS WHICH OPERATE CONTINUOUSLY AT ROOM TEMPERATURE

Double‐heterostructure GaAs–Alx Ga1−x As injection lasers which operate continuously at heat‐sink temperatures as high as 311°K have been fabricated by liquid‐phase epitaxy. Thresh‐olds for square diodes as low as 100 A/cm2 and for Fabry‐Perot diodes as low as 1600 A/cm2 have been obtained. Some details of preparation and properties are given.

Doping interface dipoles: Tunable heterojunction barrier heights and band‐edge discontinuities by molecular beam epitaxy

We have succeeded for the first time in artificially tuning the conduction and valence‐band barrier heights at an abrupt intrinsic semiconductor‐semiconductor heterojunction via a doping interface dipole (DID). This is achieved by means of ultrathin ionized donor and acceptor sheets in situ grown within ≲100 A from the heterointerface by molecular beam epitaxy. In the limit of a few atomic layers separation between the charge sheets this amounts to modify the effective band‐edge discontinuities. A near one order of magnitude enhancement in the photocollection efficiency of an abrupt AlGaAs/GaAs heterojunction has been observed as result of the conduction‐band barrier lowering induced by the DID.

Investigation of heterojunctions for MIS devices with oxygen‐doped AlxGa1−xAs on n‐type GaAs

Metal‐insulator‐semiconductor (MIS) structures were prepared with high‐resistivity oxygen‐doped Al0.5Ga0.5As layers on n‐type GaAs. These layers were grown by molecular‐beam epitaxy (MBE). Capacitance‐voltage measurements of MIS structures on both conducting and high‐resistivity substrates demonstrate the achievement of deep depletion for reverse‐bias and a near‐flatband condition at zero bias. Measurement of the output characteristics of a majority‐carrier depletion mode MISFET illustrates the application of this MIS technique to three terminal devices. The presence of a 2000‐A‐thick O‐doped Al0.5Ga0.5As layer on n‐type GaAs was found to enhance the photoluminescent intensity of the n‐GaAs layer by 52 times over that of an exposed GaAs surface. The measurements described here demonstrate that the use of single‐crystal lattice‐matched heterojunctions of O‐Al0.5Ga0.5As–n (GaAs) avoids large interface state densities. Admittance spectroscopy measurements permitted assignment of the dominant deep level in O‐...

Phase‐matched second harmonic generation in a periodic GaAs waveguide

Using a tunable laser operating near 2 μm, second harmonic generation was observed in a GaAs waveguide having a grating etched in one interface. Phase matching occurs when β2−2β1−ϑ=0, where ϑ=2π/Λ is the wave vector of the grating of period Λ and β1 and β2 are the fundamental and harmonic wave vectors.

Reduction of threshold current density in GaAs–Alx Ga1−x As heterostructure lasers by separate optical and carrier confinement

Heterostructure lasers in which the GaAs active layer is bounded on each side by successive layers of AlxGa1−xAs to confine the carriers and AlyGa1−yAs (y>x) to confine the light have been fabricated and studied. Room‐temperature threshold current densities as low as 690 ± 40 A/cm2 with differential quantum efficiencies of 32% have been obtained for 1‐mm cavity lengths.

Very high quantum efficiency GaSb mesa photodetectors between 1.3 and 1.6 μm

In this letter very high quantum efficiency GaSb mesa photodiodes with AlxGa1−xSb windows are reported for the first time. External quantum efficiencies (ηext) of ≃60% at zero bias and of ≃70% at −1 V near 1.3 μm have been obtained without antireflection coatings. More than 80% of the devices from several wafers exhibited ηext⩾50% at λ≃1.3 μm.

Back‐surface emitting GaAsxSb1−x LED’s (λ=1.0 μm) prepared by molecular‐beam epitaxy

Compositionally graded layers of GaAsxSb1−x have been grown on GaAs substrates by molecular‐beam epitaxy. Planar Zn‐diffused 50‐μm‐diam light‐emitting diodes have been prepared in GaAs0.9Sb0.1. The 1.0‐μm wavelength emission was taken out through the transparent GaAs substrate, and for a pulsed current of 100 mA, the external quantum efficiency was 0.1%.

Reduction of surface recombination current in GaAs p‐n junctions

Planar Zn‐diffused GaAs p‐n junctions have been prepared with a 2000‐A surface layer of high‐resistivity O‐doped Al0.5Ga0.5As. This surface layer significantly reduces the surface recombination current and permits the bulk diffusion current, I∝exp(qV/kT), to dominate at current densities as low as ∼5×10−3 A/cm2.

Highly Uniform Alx Ga1−x As Double‐Heterostructure Lasers and Their Characteristics at Room Temperature

Highly uniform double‐heterostructure wafers were grown reproducibly by liquid‐phase epitaxy. Thresholds and efficiencies lie within 5% for different lasers from a given wafer. Studies of the effect of dopants in the active region of lasers made from these uniform wafers showed clearly the dependence of gain and loss characteristics upon some doping parameters. External differential quantum efficiencies of 50% were obtained consistently. Peak pulse power of 6 W and cw power of 200 mW were achieved with Fabry‐Perot diodes.

Very low reach‐through voltage, high performance AlxGa1−x Sb p‐i‐n photodiodes for 1.3‐μm fiber optical systems

A high performance AlxGa1−x Sb 1.3‐μm p‐i‐n photodiode, operating at a very low reach‐through voltage (−1.5 V), has been demonstrated for the first time. The low punch‐through voltage was achieved by growing extremely low doped liquid phase epitaxial layer (ND−NA ≃4×1014/cm3). The capacitance is ≃0.4 pF and the dark current ≃20 nA at −1.5 V for a 10−4‐cm2 device area. The zero bias external quantum efficiency is ?55% at 1.3 μm; the rise time is 100 ps and the full width at half‐maximum (FWHM) is 200 ps. These results indicate that p‐i‐n photodiodes comparable in performance to homojunction InGaAs p‐i‐n detectors can be fabricated with the AlGaSb alloy system.