J.S. Osinski

Experimental study of Auger recombination, gain, and temperature sensitivity of 1.5 mu m compressively strained semiconductor lasers

The effect of strain on Auger recombination has been studied using the differential carrier lifetime technique in both lattice matched InGaAs-InP and compressively strained quaternary quantum wells. It is found that Auger recombination is reduced in strained devices. The transparency carrier density and differential gain of both lattice matched and strained devices have been obtained by gain and relative intensity noise measurement. A reduction of the transparency carrier density is observed in the strained device. However, no differential gain increase is seen. The temperature sensitivity of the threshold current density of both lattice matched and strained devices has been fully studied. Physical parameters contributing to the temperature sensitivity of the threshold current density have been separately measured, and it is shown that the change in differential gain with temperature is a dominant factor in determining the temperature sensitivity of both lattice matched and strained devices. >

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>>

Low-threshold quantum well lasers grown by metalorganic chemical vapor deposition on nonplanar substrates

Low-threshold quantum-well lasers having as-grown optical and electronic confinement fabricated by a single-step growth on nonplanar substrates are discussed. Several devices using various approaches for delineating narrow active regions by this technique are described. Fully planar index-guided arrays grown over a nonplanar substrate exhibit a threshold current of 8 mA per element. A technology called temperature engineered growth, which permits the formation of submicrometer active-region widths and wide contacting regions in the same growth step, is introduced. Lasers having active regions as narrow as 0.5 mu m grown using this technology display stable single-transverse-mode operation. CW threshold currents as low as 2.5 mA at room temperature with differential quantum efficiencies of 34%/facet were measured for uncoated devices. >

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.

Temperature engineered growth of low-threshold quantum well lasers by metalorganic chemical vapor deposition

A new technique is demonstrated for the formation of narrow active regions in quantum well lasers. In temperature engineered growth (TEG), the substrate temperature is varied during the growth of epitaxial layers by metalorganic chemical vapor deposition (MOCVD) on nonplanar substrates, allowing two‐dimensional control of device features. Buried heterostructure designs with submicron active region stripe widths are obtained without the need for fine process control of lateral dimensions. The contact area above the active region is coplanar with the surrounding surface and wide enough to allow easy contacting and heat sinking. Carrier confinement is accomplished by lateral thickness variation of the quantum well active region resulting in a local strip of minimum band gap. Lasers grown in this manner exhibit cw threshold currents as low as 3.8 mA (3.4 mA pulsed), having an as‐grown active region width of 0.5 μm. The near‐field optical profile indicates stable, single transverse mode operation and minimal c...

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>>

Quantum well lasers with active region grown by laser‐assisted atomic layer epitaxy

Laser‐assisted atomic layer epitaxy (LALE) is used to locally deposit device‐quality material for the first time, as demonstrated by successfully fabricating broad‐area lasers with a GaAs quantum well grown in this way. By hybridizing LALE with conventional metalorganic chemical vapor deposition epitaxy, heterostructures are grown which allow characterization of material quality by photoluminescence and capacitance‐voltage measurements. In addition, graded‐index separate‐confinement heterostructure lasers with threshold current densities of 650 A/cm2 for 580‐μm‐long devices were made using the LALE quantum well deposit, while devices made away from the deposit did not lase.

Low-threshold single-quantum-well InGaAs/GaAs lasers grown by metal-organic chemical vapor deposition on structure substrates

Low-threshold current (as low as 3.0 mA) and high-external efficiency ( approximately=88%) InGaAs/GaAs lasers emitting at 1 mu m under a stable fundamental transverse mode were obtained by using the temperature engineered growth technique for the growth on prepatterned substrates.<<ETX>>

Optimization of stripe width for low-threshold operation of quantum well laser diodes

An experimentally verified model for threshold current in GaAs/AlGaAs quantum well laser diodes has been extended to calculate for the first time the dependence of threshold current on stripe width. The lowest possible threshold is shown to occur when the lateral confinement factor is in the range of 55–60% for typical devices, a value that is not affected by mirror reflectivity or lateral index step. A simple, generalized optimization scheme for obtaining the unique width/length combination that results in lowest threshold is presented, and predicts potential as‐cleaved threshold currents as low as 0.5 mA.