P. Grodzinski

Low-threshold-current-density 1.5 mu m lasers using compressively strained InGaAsP quantum wells

A low-threshold current density (J/sub th/) of 140 A/cm/sup 2/ for broad-area 1.5- mu m semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm/sup -1/ and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm/sup 2/. Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J/sub th/ of 324 A/cm/sup 2/ at L=1.5 mm.<<ETX>>

Effect of Auger recombination and differential gain on the temperature sensitivity of 1.5 μm quantum well lasers

The temperature sensitivity of both strained and lattice‐matched 1.5 μm quantum well lasers has been studied. From a complete experimental investigation of the temperature behavior of carrier lifetime, gain, and internal loss, it is found that Auger recombination is not the dominant factor in affecting the temperature sensitivity of threshold currents in 1.5 μm lasers. Instead, the dominant contribution to the temperature dependence of threshold currents in 1.5 μm lasers is the change in differential gain with temperature—a characteristic not improved by strain.

Threshold current analysis of compressive strain (0-1.8%) in low-threshold, long-wavelength quantum well lasers

A comprehensive study of the effect of compressive strain on the threshold current performance of long-wavelength (1.5 mu m) quantum-well (QW) lasers is presented. Model predictions of threshold currents in such devices identify QW thickness as a parameter that must be considered in optimizing laser performance when Auger currents are present. Experimental comparisons between strained and unstrained devices reveal strain-induced reductions in internal transparency current density per QW from 66 to 40 A/cm/sup 2/, an increase in peak differential modal gain from 0.12 to 0.23 cm/A, and evidence for the elimination of intervalence band absorption as compressive strain increases from 0 to 1.8%. However, most of these improvements arise in the first approximately 1% of compressive strain. To fabricate low-threshold 1.5- mu m buried heterostructure (BH) devices in InP using the strained QW active regions an optimized design which shows that threshold current is at its lowest when the stripe width is approximately 0.6-0.7 mu m is derived. Results for uncoated BH lasers are reported. >

Low threshold current 1.5- mu m buried heterostructure lasers using strained quaternary quantum wells

Buried heterostructure lasers operating at a wavelength of 1.5 mu m with four compressively strained quaternary quantum wells (strain approximately 1.8%, thickness approximately 90 AA) and current blocking layers were made using atmospheric pressure metalorganic chemical vapor deposition. Pulsed room-temperature threshold currents for uncoated devices as low as 4.1 mA and as low as 0.8 mA for devices with high reflectivity mirror coatings are reported. The dependence of threshold current on active region width is consistent with broad-area laser measurements.<<ETX>>

CHARACTERIZATION AND DETERMINATION OF THE BAND-GAP DISCONTINUITY OF THE INXGA1-XAS/GAAS PSEUDOMORPHIC QUANTUM WELL

Single and multiple quantum well samples have been grown by atmospheric pressure metalorganic chemical vapor deposition at In compositions from 9 to 28% and layer thicknesses ranging from 15 to 140 A, depending upon the composition. Selected samples containing three quantum wells of a given composition but with different thicknesses were characterized by x‐ray double‐crystal diffractometry, low‐temperature photoluminescence, and transmission electron microscopy (TEM). Using a simulation technique based on the dynamical theory of x‐ray diffraction in concert with TEM measurements, the In composition in the quantum well as well as the thicknesses can be directly extracted. The peak positions of the photoluminescence are used to determine the strained and unstrained energy gap and the conduction band offsets associated with InxGa1−xAs of a given composition. We have found the discontinuities to be 60% of the difference in the energy gap of GaAs and strained InxGa1−xAs.

Use of tertiarybutylarsine in the fabrication of GaAs/AlGaAs quantum wells and quantum well lasers

Tertiarybutylarsine was used in the growth of GaAs and AlGaAs by metalorganic chemical vapor deposition over a range of compositions and V/III ratios. GaAs layers were obtained with both n‐ and p‐type background carrier concentrations in the low 1014 cm−3 range. AlGaAs was grown at 20, 30, and 50% compositions, and photoluminescence of the Al0.2Ga0.8As indicates high quality material with full width half maximum (FWHM) values of the peaks being comparable to arsine‐grown AlGaAs. High quality multiple Al0.3Ga0.7As/GaAs quantum wells of various widths produced photoluminescence spectra with FWHM values comparable to arsine‐grown samples. Minority‐carrier lifetimes as long as 400 ns were measured for a heterostructure of 0.5 μm GaAs with Al0.3Ga0.7As barrier layers. Graded index separate confinement heterostructure lasers were fabricated, and broad‐ area test results of these devices produced threshold current densities as low as 186 A/cm2.

Experimental verification of strain benefits in 1.5- mu m semiconductor lasers by carrier lifetime and gain measurements

Recombination processes, gain, and loss have been comparatively studied in both strained and lattice-matched 1.5- mu m semiconductor quantum-well lasers using differential carrier lifetime techniques and other measurements. For the first time, some predicted strain benefits to 1.5- mu m semiconductor lasers have been verified, including (i) the reduction of the Auger recombination rate in devices with both 0.9% and 1.8% compressive strain; and (ii) a 33% reduction of transparency carrier density in lasers with 0.9% strain compared to lattice-matched lasers. The authors, however, did not observe an increase of the differential gain in strained devices as predicted.<<ETX>>

Comparative study of low-threshold 1.3 mu m strained and lattice-matched quantum-well lasers

A study of the effects of biaxial strain on the performance of low-threshold 1.3- mu m In/sub x/Ga/sub 1-x/As/sub y/P/sub 1-y//InP quantum-well lasers is presented. Lasers with lattice-matched, compressive-strained, and tensile-strained quantum-wells were fabricated to compare the effect of strain on various device parameters. Threshold current densities as low as 187 A/cm/sup 2/ for a two-quantum-well device with 0.85% compressive strain were obtained.<<ETX>>

Photoluminescence study of critical thickness of pseudomorphic quantum wells grown on small area mesa stripes

Pseudomorphic In0.18Ga0.82As single quantum wells (QWs) have been grown by metalorganic chemical vapor deposition (MOCVD) on patterned substrates with mesa sizes of 3.5 μm oriented along [110] and [110] directions. Using a post‐growth masking technique, photoluminescence (PL) has been used to characterize the optical properties of the as‐grown QWs. Our results show the increase of the critical thickness by about 50% for growth on [110] undercut mesa as compared with that on the planar substrate due to the discontinuous growth behavior and no increase of critical thickness of [110] oriented mesas due to the continuous growth behavior and outdiffusion of In from the facet wall of the groove to the mesa top.

Growth of InP related compounds on structured substrates for the fibrication of narrow stripe lasers

MOCVD growth of InP/InGaAs/InGaAsP multilayer structures on patterned substrates with mesa stripes etched along [110] and [110] crystallographic directions has been investigated. Twinning was found on the groove wall facets for [110 patterns. Twinning alters both growth rate and growth directionality of the layers grown on the mesa top. Structures grown on [110] oriented patterns revealed a discontinuity of the growth between the top of the mesa and the groove region. This isolates the layers grown on the mesa top and allows the fabrication of narrow stripe, buried heterostructure lasers. Both double heterostructure and quantum well structure devices have been fabricated. DH structures with a stripe width of 3 μm exhibited a laser threshold current of 54 mA, while quantum well devices with four strained In0.66Ga0.34As wells and stripe width of 2 μm lased at 35 mA.