E. I. Chen

Native oxide top- and bottom-confined narrow stripe p-n AlyGa1-yAs-GaAs-InxGa1-xAs quantum well heterostructure laser

A new form of AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well heterostructure (QWH) laser that is confined above and below the active region by an insulating low refractive index native oxide is demonstrated. The laser diodes are defined from a mesa edge by the selective lateral oxidation and anisotropic oxidation of high Al composition AlyGa1−yAs layers (y=0.85, 0.87) located above and below the QW and waveguide active region. This structure provides excellent current and optical confinement, resulting in continuous wave threshold currents of ∼8 mA and maximum output powers (uncoated laser) of 35 mW/ facet for a∼2.5 μm aperture.

AlxGa1−xAs–GaAs metal–oxide semiconductor field effect transistors formed by lateral water vapor oxidation of AlAs

Data are presented demonstrating a GaAs‐based metal–oxide semiconductor field effect transistor employing in the gate region a laterally formed native oxide of AlAs. The gate oxide, formed by a water vapor process, is similar to that used successfully in recently developed semiconductor laser devices. The transistors described here represent an extension of the ‘‘wet’’ oxidation Al‐based III–V native oxide technology employed successfully in light‐emitting and laser devices.

Photopumped room‐temperature edge‐ and vertical‐cavity operation of AlGaAs‐GaAs‐InGaAs quantum‐well heterostructure lasers utilizing native oxide mirrors

Data are presented on the 300‐K continuous and pulsed photopumped laser operation of AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum‐well heterostructure (QWH) crystals that utilize large‐index‐step high‐contrast distributed Bragg reflector mirrors. The mirrors are formed by selective lateral oxidation (H2O+N2, 425 °C) of three lower and three upper AlAs layers in the structure, resulting in enhanced cavity Q in the vertical direction. The laterally oxidized mirrors, a small lower and an upper ‘‘stack’’ that sandwich a lateral waveguide and double QW active region, are of sufficient quality to permit vertical‐cavity laser operation of the QWH crystals.

Effects of low‐temperature annealing on the native oxide of AlxGa1−xAs

Data are presented on the effects of low‐temperature (∼540 °C) annealing, with and without an As overpressure, on the native oxide of AlxGa1−xAs formed via water vapor oxidation at elevated temperature (∼425 °C). Auger electron spectroscopy data show the Al to be oxidized while the Ga remains unoxidized after the water vapor oxidation of AlxGa1−xAs. Transmission electron microscopy data show a possible composition or phase change upon annealing with an As overpressure. Electron diffraction data indicate that the as‐oxidized AlxGa1−xAs is a combination of four possible phases of Al2O3, η, γ, δ, χ, or AlO(OH). Supporting secondary‐ion mass spectrometry data are also presented. Ellipsometer measurements indicate an index of refraction n=1.63 (λ=6328 A) for the native oxide. Ellipsometer measurements of the oxidized and annealed samples show the creation of a region 300–550 A thick at the oxide‐semiconductor interface with n=2.78–2.93.

Native oxide‐embedded AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well heterostructure lasers

Data are presented on the photopumped laser operation of an AlAs‐AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well heterostructure in which the GaAs‐InxGa1−xAs active region is embedded, top and bottom, in native oxide. The upper and lower wider gap confining regions of the laser are selectively converted to oxide, leaving the active region intact. The oxidation (H2O+N2, 425 °C) proceeds laterally (perpendicular to the crystal growth direction) from a chemically etched mesa edge. The photopumped oxide‐embedded heterostructure operates as a laser continuously at 77 K and pulsed at 300 K. In comparison with the as‐grown crystal, the oxidized sample shows no significant laser threshold degradation.

Visible‐spectrum (λ=650 nm) photopumped (pulsed, 300 K) laser operation of a vertical‐cavity AlAs–AlGaAs/InAlP–InGaP quantum well heterostructure utilizing native oxide mirrors

Data are presented on the 300 K photopumped (pulsed) laser operation of a visible‐spectrum (λ=650 nm) AlAs–AlGaAs/InAlP–InGaP quantum‐well heterostructure (QWH) crystal that utilizes high‐index‐contrast AlAs‐native‐oxide/Al0.6Ga0.4As distributed Bragg reflector mirrors. The mirrors are formed by the lateral oxidation (H2O+N2, 425 °C) of two sets of four ‘‘buried’’ AlAs layers that are separated by Al0.6Ga0.4As. These mirrors, which create a high‐Q cavity in the vertical direction, ‘‘sandwich’’ a one‐wavelength InAlP–InGaP QW active region, thus forming a compact microcavity that ‘‘tunes’’ the carrier scattering and recombination into a narrow spectrum (∼25 A) and supports laser operation in the vertical direction.

EDGE-EMITTING QUANTUM WELL HETEROSTRUCTURE LASER DIODES WITH AUXILIARY NATIVE-OXIDE VERTICAL CAVITY CONFINEMENT

Data are presented demonstrating edge‐emitting laser diode operation of AlyGa1−yAs– GaAs–InxGa1−xAs quantum well heterostructures modified by the formation of a buried native‐oxide distributed Bragg reflecting (DBR) mirror adding vertical confinement to the longitudinal laser cavity. The bottom DBR mirror, combined with the highly reflective top p‐contact metallization (Ag), forms a thin broadband vertical cavity. The auxiliary vertical mirrors are tuned to improve the coupling of the spontaneous emission to the longitudinal lasing mode, resulting in reduced threshold currents and modified emission characteristics below threshold.

High current density carbon‐doped strained‐layer GaAs (p+)‐InGaAs(n+)‐GaAs(n+) p‐n tunnel diodes

Data are presented showing that a GaAs p‐n tunnel diode can be modified, and improved, with the introduction of an InxGa1−xAs layer (Lz∼100 A) in the barrier region to reduce the energy gap (and carrier mass) and increase the tunneling probability without sacrificing the high injection barrier and voltage of GaAs. Peak tunnel current densities in the range (1–1.5)×103 A/cm2 are obtained, with peak‐to‐valley current ratios of ∼20:1 and voltage ‘‘swings’’ from peak tunnel current to equal injection current of ≳1 V (≤1 V for GaAs). The C‐doped GaAs(p+)‐InGaAs(n+)‐GaAs(n+) diodes are grown by metalorganic chemical vapor deposition and are compared to GaAs tunnel diodes fabricated by the usual alloy process (i.e., local liquid phase epitaxy).

n‐p‐(p+‐n+)‐n AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum‐well laser with p+‐n+ GaAs‐InGaAs tunnel contact on n‐GaAs

Data are presented on the growth, by metalorganic chemical vapor deposition, and fabrication of n‐p (n‐up) AlGaAs‐GaAs‐InGaAs quantum‐well heterostructure lasers using a p+‐n+ GaAs‐InGaAs reverse‐biased tunnel junction to contact the n‐type GaAs substrate. The lasers operate continuously at 300 K with a threshold of ∼37 mA for a 10‐μm‐wide native‐oxide‐defined gain‐guided stripe (cavity length ∼375 μm). Comparison tunnel junctions similar to those used in the diode lasers are also fabricated and exhibit low reverse‐biased series resistances (∼2.2 Ω, area ∼4.5×larger).

Deep‐oxide planar buried‐heterostructure AlGaAs–GaAs quantum well heterostructure laser diodes

Data are presented on deep‐oxide planar buried‐heterostructure AlGaAs–GaAs quantum well heterostructure laser diodes fabricated using a self‐aligned process that combines native oxide and impurity‐induced layer disordering (IILD) technologies. Silicon IILD intermixes the waveguide layers on either side of an active area stripe and allows ‘‘wet’’ oxidation to penetrate and create a low‐index (n∼1.7) deep‐oxide structure for electrical and optical confinement. Continuous‐wave (cw) threshold currents of ∼3.4 mA are measured for ∼3.5‐μm‐wide active regions (L∼250 μm), with maximum cw output powers greater than 29 mW/facet and external differential quantum efficiencies as high as 70% (300 K, uncoated facets).