T. L. Paoli

Stripe‐geometry quantum well heterostructure AlxGa1−xAs‐GaAs lasers defined by defect diffusion

Impurity‐free selective layer disordering, utilizing Si3N4 masking stripes and SiO2 defect (vacancy) sources, is used to realize room‐temperature continuous AlxGa1−xAs‐GaAs quantum well heterostructure lasers.

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.

Strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures and quantum-well laser diodes

The properties of (AlGa)/sub 0.5/In/sub 0.5/P, strained Ga/sub x/In/sub 1-x/P/(AlGa)/sub 0.5/In/sub 0.5/P heterostructures, and single quantum well (QW) laser diodes with Al/sub 0.5/In/sub 0.5/P cladding layers, prepared by low pressure organometallic vapor phase epitaxy, are described. The influence of biaxial strain upon the relative positions of the valence band edges are examined by analyzing the polarized spontaneous emission. Laser diodes with wavelength 620 >

Wavelength modification of AlxGa1−xAs quantum well heterostructure lasers by layer interdiffusion

Data are presented showing that thermal annealing (875–‐900 °C) can be used to modify the wavelength of a photopumped, low threshold AlxGa1−xAs quantum well heterostructure (QWH) laser from ∼8200 to ∼7300 A with a threshold change from 150 to 1700 W/cm2. The energy levels of the annealed single quantum well crystal are approximated by fitting a modified Poschl–Teller potential to the band‐edge profile as modified by layer (Al–Ga) interdiffusion. The layer (Al–Ga) interdiffusion coefficient (at 875 °C) is found to be smaller, by a factor of 3–4, than previously reported. We suggest that this is due to the high quality, i.e., low defect density, of the ultralow threshold QWH crystals of this work.

Monolithic waveguide coupled cavity lasers and modulators fabricated by impurity induced disordering

Describes results on AlGaAs integrated optoelectronic devices consisting of combinations of buried passive waveguide regions with active multiple quantum well gain regions. The authors have developed a technique for accomplishing this integration in which the waveguide regions have greatly reduced propagation loss at the gain wavelength of the active media. They have incorporated sections of waveguide into laser cavities, and the resulting low (7-11 mA) threshold currents and weak dependence of threshold current on waveguide length confirm the reduced loss and waveguiding nature of the waveguide regions. They have used these structures to monolithically couple laser amplifiers to electroabsorption modulators. Among their results on these devices are electroabsorption modulators with contrast ratios of 23:1 and monolithic Q-switch operation resulting in pulse widths of less than 200 ps. The relative simplicity with which these structures are fabricated via impurity induced disordering techniques promises to result in major impact on practical systems for monolithic integration. >

Low threshold planar buried heterostructure lasers fabricated by impurity‐induced disordering

We report on the fabrication of index‐guided buried heterostructure lasers by the process of silicon impurity‐induced disordering. This fabrication process for a buried heterostructure laser offers the advantage of reduced fabrication complexity over previous fabrication methods. We present measurements that demonstrate the operation of these devices in a single longitudinal mode, fundamental transverse mode, and with cw threshold currents as low as 3 mA. We also have extracted 80 mW cw from a device with a 10‐mA threshold current. Our results indicate that this process has great potential for the fabrication of low threshold, efficient light sources.

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).

Observation of supermodes in a phase‐locked diode laser array

Phase‐locked diode laser arrays have been observed to oscillate in collective modes (supermodes) characteristic of a composite waveguide formed as a result of optical coupling between the fields of individual waveguides in the array. For an array of 11 gain‐guided lasers, as many as five different supermodes oscillated simultaneously at wavelengths separated by approximately 0.3 A. Each supermode was identified by spectrally resolving the spatial profile of the optical intensity on the laser facet.

Stripe‐geometry AlGaAs‐GaAs quantum‐well heterostructure lasers defined by impurity‐induced layer disordering

Stripe‐geometry AlGaAs‐GaAs single quantum‐well heterostructure lasers are demonstrated in which the region complementary to the stripe (outside of and defining the stripe) is shifted to higher band gap, and lower refractive index, by low‐temperature (600 °C) Zndiffusion. Impurity‐induced Al‐Ga interdiffusion causes the single GaAsquantum well (x=0, L z ≊80 A) outside of the stripe region to be mixed (‘‘absorbed,’’ x→x′) into the Al x′Ga1−x′As (x′∼0.3, L z′≊0.18 μm) bulk‐layer waveguide of the crystal.

High power (2.1 W) 10‐stripe AlGaAs laser arrays with Si disordered facet windows

Silicon impurity induced disordering has been used to fabricate lasers with reduced facet absorption (facet windows) exhibiting enhanced catastrophic facet damage levels over comparable nonwindow devices. Power levels of 1.2 W cw were obtained from uncoated output facet devices and 2.1 W cw were obtained for a device with a coated output facet. Evidence is presented that the window region formed by silicon diffusion is a low‐loss waveguide which confines the propagating wave, increasing the efficiency of the device.