Stripe-geometry Double-heterostructure Lasers Research Articles

Selectively embedded growth by chemical beam epitaxy for the fabrication of InGaAs/InP double-heterostructure lasers

In order to fabricate InGaAs/InP double-heterostructure (DH) lasers, a novel selectively embedded one-step growth by chemical beam epitaxy (CBE) was adopted. Before the selective CBE growth, 6–8 μm wide channels on an n-InP substrate were undercut by wet chemical etching through a 170 nm thick SiO2 film mask. A 6 μm wide stripe-geometry DH laser structure with an active layer of 0.14 μm thickness was grown selectively with good planarity into the channels and operated by a pulse.

HgCdTe infrared diode lasers grown by MBE

The authors report their latest results on the fabrication and successful operation of HgCdTe infrared diode lasers. The stripe-geometry double-heterostructure lasers were grown by molecular beam epitaxy (MBE). The active layer thickness ranges between 0.9 and 1.4 mu m, and the p+ and n+ confinement layers were in situ doped up to 1018 cm-3 with arsenic and indium, respectively. Five double heterostructures were grown, all of which produced working lasers. The devices were operated under pulsed currents at temperatures between 40 and 90 K. The 77 K stimulated emission wavelengths for these lasers were 2.9, 3.4, 3.9 and 4.4 mu m. Operation at 5.3 mu m was demonstrated at 60 K. The lowest 77 K threshold current density was 419 A cm-2 which is very close to the prediction of a numerical calculation. Characterization of the devices, including, for example, temperature dependence of the threshold currents and spectral analysis, was performed and showed the characteristics of well-behaved, stable devices that operated without failure while being tested.

HgCdTe double heterostructure injection laser grown by molecular beam epitaxy

While a variety of light-detecting devices have been made with HgCdTe, little has been done to apply this technology to light-emitting devices. We report here the successful fabrication and operation of the first HgCdTe injection laser. This stripe-geometry double-heterostructure laser was operated under pulsed current at temperatures between 40 and 90 K. At 77 K, the emission wavelength was 2.86 μm with a linewidth of 0.3 meV, and the pulsed threshold current density was 625 A/cm2. The double heterostructure, with a 1.4-μm-thick active layer, was grown and in situ doped by molecular beam epitaxy (MBE). The p+ and n+ confinement layers were doped with arsenic and indium, respectively.

A generalized thermal model for stripe-geometry injection lasers

We present a generalized thermal model based on a finite-element code for estimating the temperature rise, associated thermal resistance, and cw optical power in a stripe-geometry double-heterostructure laser. In particular, we report the first thermal analysis of a zinc-diffused, oxide-insulated AlGaAs laser structure below and above threshold taking into account the lateral current spreading, the temperature dependence of the threshold current, and external differential quantum efficiency. The results show that the thermal resistance of the device increases approximately by 18% with the effects of zinc diffusion and oxide insulation.

Effect of index antiguiding on the far-field distribution of stripe-geometry lasers

The dependence of the threshold far-field behavior on the stripe width and index antiguiding is investigated theoretically using realistic carrier-density profiles in stripe-geometry double-heterostructure lasers. It is suggested that for lasers exhibiting twin lobes in their far-field the peak separation can be used to estimate the extent of index antiguiding. The results indicate that the thershold for the appearance of far-field lobes in narrow stripe lasers can be pushed to a higher drive-level by shortening the cavity or by decreasing the facet reflectivity.

Effect of Nonuniformity in Temperature Distribution in a Stripe-Geometry Double-Heterostructure Laser

The effect of nonuniformity in temperature distribution on the lateral mode guiding in a stripe-geometry double-heterostructure laser is investigated theoretically with the aid of a mathematical model which properly takes into account lateral current spreading, carrier diffusion, two-dimensional heat diffusion, and the variations of gain and refractive index parallel to the junction planes. The effective dielectric constant method, with parabolic approximation, was used in solving the resulting two-dimensional wave equation. Calculated results, which are generally in reasonably good agreement with existing experimental data, show that lateral thermal guiding may exist, in addition to gain-guiding for CW operation.

Waveguiding in stripe-geometry diode lasers with power-law profiles

Simple closed-form expressions are derived for the modal propagation constant and field intensity of stripe-geometry double-heterostructure laser diodes with dielectric profiles of the form ε(x) = ε(0)−Δε‖x/w‖α. These expressions are useful for analyzing near-field and far-field data when the parabolic approximation is not sufficiently accurate.

Spectral characteristics of external-cavity controlled semiconductor lasers

Experiments with an external-cavity semiconductor laser indicate that single-frequency oscillation may be obtained in an injection laser when the gain is temporally and spatially stabilized within the active region. Using an originally multimode laser diode as the gain medium, the external-cavity laser oscillates stably in the fundamental spatial mode and in a single longitudinal mode with a frequency which is tunable over a 10 nm spectral range. The rms frequency jitter of the unstabilized laser is 500 kHz. These mode characteristics suggest that spatially inhomogeneous gain saturation is significant only in the lateral direction in the active region of a stripe-geometry double-heterostructure laser diode. A quantitative analysis of the spontaneous emission in the spectral vicinity of the lasing mode shows no evidence of spectral hole burning, with a 0.5 percent upper limit to the depth of the hole burned in the gain spectrum by a lasing mode power of 5 mW.

Low threshold Be implanted (GaAl)As laser on semi-insulating substrate

Be implanted stripe geometry double heterostructure lasers have been fabricated on a semi-insulating GaAs substrate, with threshold currents as low as 15 mA for a cavity length of 100 μm. The laser has been monolithically integrated with a metal-semiconductor field-effect transistor.

Lateral waveguiding in stripe-geometry double-heterostructure lasers below the lasing threshold

Structure in the far-field pattern of current-confined stripe-geometry double-heterostructure lasers in the angle range \pm 20\deg is observed at current levels of less than \frac{1}{4} of threshold value. The behavior is explained by leaky-mode guiding due to a gain maximum under the stripe and to a negative refractive index step on the order of -0.01.

The effects of processing stresses on residual degradation in long-lived Ga1−xAlxAs lasers

Oxide-insulated stripe-geometry double-heterostructure lasers have been lifetested continuously for periods up to 25 000 h. Degradation occurred in two stages, an initial stage lasting several thousand hours and a final stage, characterized by rates of threshold increase of 0–6 and 1–2%/kh, respectively. The dominant stress in these lasers is caused by the insulating oxide film. The magnitude of the stress was found to vary considerably depending on the detailed shape of the oxide profile and thickness. Good correlation was found between stress magnitude and initial residual degradation rate. It is concluded that for reliable laser performance processing stresses must not exceed 1×108 dyn cm−2 in the active region.

Thermal-resistance models for proton-isolated double-heterostructure lasers

Calculations of the thermal resistances of stripe-geometry double-heterostructure lasers are dependent on assumptions made concerning the positions of heat sources within the laser structures. The effect on thermal resistance of heat sources located at various levels in the multilayer structure are considered here. The calculations indicate that thermal resistances of proton-isolated structures can be approximately halved when energy is radiatively transferred from the device active region rather than when all heat is generated within the device active region. This should be taken into consideration when the experimental effectiveness of laser-dice-bonding technology is being evaluated.

GaAs lasers with consistently low degradation rates at room temperature

Simple oxide-insulated stripe-geometry double-heterostructure lasers have been made and life tested as part of an extensive laser reliability program. Early lasers have now been on test for more than 13 000 h and the first batch test has exceeded 7000 h. All the batch test lasers show slow degradation and at least 85% have rates of increase of threshold below 3.3% per 1000 h. Simple visual prebonding selection was used to eliminate defective lasers, and these results demonstrate that within this limitation lives in excess of 7000 h can be consistently achieved.

Enhanced localized degradation and anomalous emission spectra of Ga1−xAlxAs double heterostructure lasers induced by fabrication processes

Oxide-insulated stripe geometry double heterostructure lasers have been fabricated with and without a deep (1.3 μm) zinc diffusion prior to alloyed contacting. The two processes were found to result first in emission spectra indicative of significant differences in the point defect complex densities in the device active regions, and second in distinctly different modes of dark effect degradation.

Monolithic Passivated Stripe Geometry Double Heterostructure Injection Lasers by Selective Chemical Etching

Stripe geometry double heterostructure lasers fabricated by selective chemical etching in a monolithic way and passivated on the resonator mirrors are described. The method of etching and the results of the characteristics of the lasers fabricated by the etching which uses the alignment of a rectangular etching mask with <100> direction in a {100} wafer are shown. The lowest threshold current density of the lasers fabricated is about 4.5 kA/cm2. A novel method of selective etching with alignment of a rectangular mask with <110> direction in a {100} wafer which produce very smooth nearly {100} facet planes appearing at the four side corners of the rectangular etched island is also described.

Near- and far-field emission distributions of mesa stripe geometry double heterostructure lasers

Mesa stripe geometry double heterostructure lasers have been made with cavity widths down to 16 μm. The lowest threshold current values are down to 75 mA but more typical values are 110 mA, and the slope efficiencies are typically 40%. Measurements of near- and far-field distributions have shown that the problem of high order mode structure parallel to the junction is not as serious as expected although emission is normally in the lowest order only for very low drive currents. Improved mode control is demonstrated by a hybrid mesa-contact stripe geometry device which gave a pulse power output of 30 mW in the lowest order mode at a drive current of 310 mA.