T. A. Richard

Bio: T. A. Richard is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Quantum well & Heterojunction. The author has an hindex of 11, co-authored 17 publications receiving 827 citations.

Hydrolyzation oxidation of AlxGa1−xAs‐AlAs‐GaAs quantum well heterostructures and superlattices

Abstract: Data are presented on the conversion (selective conversion) of high‐composition (AlAs)x(GaAs)1−x layers, e.g., in AlxGa1−xAs‐AlAs‐GaAs quantum well heterostructures and superlattices (SLs), into dense transparent native oxide by reaction with H2O vapor (N2 carrier gas) at elevated temperatures (400 °C). Hydrolyzation oxidation of a fine‐scale AlAs(LB)‐GaAs(Lz) SL (LB +Lz≲100 A), or random alloy AlxGa1−xAs (x≳0.7), is observed to proceed more slowly and uniformly than a coarse‐scale ‘‘alloy’’ such as an AlAs‐GaAs superlattice with LB + Lz≳200 A.

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

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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).

Native‐oxide masked impurity‐induced layer disordering of AlxGa1−xAs quantum well heterostructures

Abstract: Data are presented showing that the native oxide that can be formed on high Al composition AlxGa1−xAs (x≳0.7) confining layers on AlyGa1−yAs‐AlzGa1−zAs (y≳z) superlattices or quantum well heterostructures serves as an effective mask against impurity diffusion (Zn or Si), and thus against impurity‐induced layer disordering. The high quality native oxide is produced by the conversion of high Al composition AlxGa1−xAs (x≳0.7) confining layers, which can be grown on a variety of heterostructures, via H2O vapor oxidation (≳400 °C) in an N2 carrier gas.

Native-Oxide Defined Ring Contact for Low Threshold Vertical-Cavity Lasers

Abstract: Data are presented characterizing a new process for fabrication of vertical‐cavity surface‐emitting lasers based on the selective conversion of high Al composition epitaxial AlGaAs to a stable native oxide using ‘‘wet oxidation.’’ The native oxide is used to form a ring contact to the laser active region. The resulting laser active regions have dimensions of 8, 4, and 2 μm. The lowest threshold laser is achieved with the 8‐μm active region, with a minimum threshold current of 225‐μA continuous wave at room temperature.

Selectively oxidised vertical cavity surface emitting lasers with 50% power conversion efficiency

Abstract: Index-guided vertical cavity top-surface emitting laser diodes have been fabricated from an all epitaxial structure with conducting mirrors by selective lateral oxidation of AlGaAs At low voltage, a 78% slope efficiency, and a 350 mu A threshold current in a single device combine to yield a maximum power conversion efficiency of 50% at less than a 2 mA drive current The device operates in a single mode up to 15 mW >

Ultralow threshold current vertical-cavity surface-emitting lasers obtained with selective oxidation

Abstract: The authors report InGaAs single quantum well vertical-cavity surface-emitting lasers with an intracavity p-contact fabricated by selective oxidation of AlAs and distributed Bragg reflectors composed of binary materials (AlAs/GaAs). Record low threshold currents of 8.7 µA in ~3 µm square devices and 140 µA in 10 µm square devices with maximum output powers over 1.2 mW are achieved.

Low threshold voltage vertical-cavity lasers fabricated by selective oxidation

Abstract: Novel vertical-cavity surface emitting lasers fabricated using selective oxidation to form a current aperture under a top monolithic distributed Bragg reflector mirror are reported. Large cross-sectional area lasers (259 µm2) exhibit threshold current densities of 150 A/cm2 per quantum well and record low threshold voltage of 1.33 V. Smaller lasers (36 µm2) possess threshold currents of 900 µA with maximum output powers greater than 1 mW. The record performance of these oxidised vertical-cavity lasers arises from the low mirror series resistance and very efficient current injection into the active region.