J. E. Epler

Effects of dielectric encapsulation and As overpressure on Al‐Ga interdiffusion in AlxGa1−x As‐GaAs quantum‐well heterostructures

Data are presented showing that the Al‐Ga interdiffusion coefficient (DAl‐Ga) for an AlxGa1−xAs‐GaAs quantum‐well heterostructure, or a superlattice, is highly dependent upon the crystal encapsulation conditions. The activation energy for Al‐Ga interdiffusion, and thus layer disordering, is smaller for dielectric‐encapsulated samples (∼3.5 eV) than for the case of capless annealing (∼4.7 eV). The interdiffusion coefficient for Si3N4‐capped samples is almost an order of magnitude smaller than for the case of either capless or SiO2‐capped samples (800≤T≤875 °C). Besides the major influence of the type of encapsulant, the encapsulation geometry (stripes or capped stripes) is shown, because of strain effects, to be a major source of anisotropic Al‐Ga interdiffusion.

Room‐temperature continuous operation of p‐n AlxGa1−xAs‐GaAs quantum well heterostructure lasers grown on Si

We describe the construction and room‐temperature (300 K) continuous (cw) operation of p‐n diode Al x Ga1−x As‐GaAs quantum wellheterostructure (QWH) lasers grown on Si substrates. The QWH crystal is grown in two stages, the first part by molecular beam epitaxy(MBE) and the single‐well quantum well active region by metalorganic chemical vapor deposition(MOCVD). Simple gain‐guided stripe configuration lasers fabricated on the MBEMOCVD QWH wafer operate cw at 300 K and have pulsed thresholds as low as 1.8×103 A/cm2.

Laser induced disordering of GaAs‐AlGaAs superlattice and incorporation of Si impurity

A scanned Ar+ laser beam is demonstrated to be an effective way to selectively disorder very localized regions of an AlGaAs‐GaAs superlattice. As the focused laser beam scans across the sample, the superlattice rapidly melts and then regrows. Scanning electron microscope images of the scan cross section show a micron‐sized region of nearly homogeneous composition with a sharp (<400 A) transition to as‐grown superlattice material. In addition, dopants such as Si deposited on the surface in an encapsulation layer are incorporated into the melt in high concentrations during the scanning process. In this way, the recrystallized material can serve as a patterned source for impurity induced disordering during a standard thermal anneal. The depth and width of the disordered region are given as a function of laser power measured before and after the thermal anneal (850 °C, 6 h).

Stability of 300 K continuous operation of p‐n AlxGa1−xAs‐GaAs quantum well lasers grown on Si

Data are presented on p‐n (diode) AlxGa1−xAs‐GaAs quantum well lasers grown on Si indicating that continuous 300 K operation is possible for four or more hours. Lower threshold diodes (1.4 kA/cm2) of given dislocation density are not necessarily as stable as higher threshold diodes (1.8 kA/cm2) of lower dislocation density, ∼10 min vs ≳4 h. Stability data on diodes agree with the behavior of photopumped samples of the same crystals with the Si substrates removed.

Impurity-disordered, coupled-stripe AlxGa1−xAs-GaAs quantum well laser

Continuous room‐temperature operation of impurity‐disordered, coupled‐stripe Al x Ga1−x As‐GaAs quantum wellheterostructure lasers is described. Silicon (donor) diffusion at 850 °C is used to produce layer disordering and index guiding, in addition to providing carrier confinement in a ten‐stripe coupled array (8‐μm‐wide stripes on 10‐μm centers).

AlGaAs multiple-wavelength light-emitting bar grown by laser-assisted metalorganic chemical vapor deposition

The first optical device fabricated from epitaxial material grown by laser‐assisted crystal growth is reported. The device is an AlGaAs multiple‐wavelength light‐emitting bar in which the Al composition of the active layer, and thus the emission wavelength, varies as a function of position along the bar. The Al composition is photochemically patterned during growth with an in situ Ar+ laser beam. The energy band gap increases from a minimum of 1.475 eV to a maximum of 1.52 eV over a 4 mm section of the bar. The spatial dependence of the energy band gap is roughly Gaussian and corresponds to the laser intensity profile. The electroluminescent data are presented along with a brief discussion of the laser‐assisted crystal growth process.

Effects of microcracking on AlxGa1-xAs-GaAs quantum well lasers grown on Si

Data are presented demonstrating continuous (cw) 300 K operation of p‐n AlxGa1−xAs‐GaAs quantum well heterostructure lasers grown on Si and fabricated with naturally occurring microcracks running parallel to or perpendicular to the laser stripe. Operation for over 17 h is demonstrated for a diode with a parallel microcrack inside the active region. Diodes with microcracks perpendicular to the laser stripe exhibit relatively ‘‘square’’ light output versus current (L‐I) characteristics and spectral behavior indicating internal reflections involving coupled multiple (internal) cavities. The lasers have operated (cw, 300 K) as long as 16 h.

Thermal behavior and stability of room‐temperature continuous AlxGa1−xAs‐GaAs quantum well heterostructure lasers grown on Si

Data are presented on the thermal characteristics of p‐n AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) diode lasers grown on Si substrates. Continuous 300‐K operation for over 10 h is demonstrated for lasers mounted with the junction side away from the heat sink (‘‘junction‐up’’) and the heat dissipated through the Si substrate. ‘‘Junction‐up’’ diodes that are grown on Si substrates have measured thermal impedances that are 38% lower than those grown on GaAs substrates, with further reductions possible. Thermal impedance data on ‘‘junction‐down’’ diodes are presented for comparison. Measured values are consistent with calculated values for these structures. Low sensitivity of the lasing threshold current to temperature is also observed, as is typical for QWH lasers, with T0 values as high as 338 °C.

Monolithic integration of a transparent dielectric waveguide into an active laser cavity by impurity-induced disordering

In this letter we report the successful combination of a low‐loss buried waveguide providing two‐dimensional optical confinement with an active gain medium. We have thereby realized a planar and monolithic composite cavity laser where the laser cavity consists of distinct regions of optical gain combined with distinct regions of low‐loss optical waveguide. The low threshold currents of these strucures (<10 mA) confirm the low loss and waveguiding nature of the waveguide regions. The ability to make these types of structures has applications for window lasers, monolithic waveguides, and monolithic integration of electrical and optical components.

Continuous (300 K) photopumped laser operation of AlxGa1−xAs‐GaAs quantum well heterostructures grown on strained‐layer GaAs on Si

Data are presented demonstrating continuous (cw) room‐temperature photopumped laser operation of an AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) grown on a Si substrate. The QWH is grown in a two‐step process with first the GaAs grown on the Si substrate by molecular beam epitaxy (MBE) and second the QWH grown by metalorganic chemical vapor deposition (MOCVD). The MBE GaAs contains a thin 600‐A layer at the Si/GaAs interface that is rich in defects, ‘‘absorbs’’ much of the mismatch, and provides a good surface (specular surface) for the MOCVD growth of the QWH. Although cw 300 K laser operation is obtained, it occurs at high threshold and is short lived, agreeing with earlier results on the cw 300 K laser operation of mismatched III‐V QWH’s.