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We demonstrate GaSb-based diode lasers emitting near 2.7 μm that are fabricated as on-chip unstable resonator cavities using the focused ion beam tool. A near-diffraction-limited lateral beam is observed in broad-area devices where the reflection from the cylindrical mirror at the back facet overrides direct counterpropagation in the cavity to suppress the formation of filaments. We identify a geometric parameter that can be used as a general guide to optimizing the on-chip unstable resonator cavity for maximum brightness. This parameter is the aperture within the unstable resonator cavity, a measure of the angular divergence contained within the device, and is shown to correlate with the onset of filament suppression. [ABSTRACT FROM AUTHOR]

The focused ion beam milling tool was used to convert a GaSb-based broad area gain-guided quantum well laser device with a standard Fabry-Pérot cavity into one with an unstable resonator cavity. A cylindrical mirror was formed at the back facet of the broad area device emitting near 2 μm. Compared to the Fabry-Pérot cavity device, where the coherency of the beam is severely disrupted by filamentation, the unstable resonator cavity device exhibits an ~2× diffraction limited beam. The relatively small penalty in slope efficiency demonstrates that a much higher brightness can be reached in this class of broad area devices. [ABSTRACT FROM AUTHOR]

Research describing the photoluminescent properties of strained layer superlattice samples is presented. Fourier transform infrared absorbance spectroscopy is studied for various thicknesses of GaSb layers.

Research describing an antimonide-based digital alloy laser is presented. In particular the use of modulated molecular beam epitaxy for quantum well and barrier growth on the laser structure is investigated.

Photoluminescence (PL) spectroscopy is used to characterize GaAs1-xSbx, which is grown on InP substrates with the help of molecular beam epitaxy. Bound exciton and quasi-donor-acceptor transitions are observed in the PL spectrum. Excitation intensity-dependent transition energy is used to determine composition modulation in the epitaxial layers. Misfit relaxation produces concentration modulation which induces a large Stokes shift.

We compare the performance of several optically pumped unstable resonator semiconductor lasers with cavity lengths of 4, 5, and 6 mm and operating in the mid-IR at 4.7 μm. The unstable resonator lasers (URLs) were fabricated by polishing a diverging cylindrical mirror on one of the facets. In general, the URL beam quality (BQ) was 1–2 times diffraction limited when operated at pump powers below 30 W (URL power ≤6 W) As the pump power is increased, the BQ is observed to degrade; at 60 W the URL’s were ∼3.5 times diffraction limited (URL power ≈11 W). The highest brightness URL, a 4-mm long device, was compared with an equivalent 4-mm long Fabry–Perot (FP) laser operated at different cavity widths. The performance of the broad area URL (500 μm width), as assessed by power-in-the-bucket measurements, was superior to both wide stripe (500 μm) and narrow pump stripe (100 μm) FP lasers. [ABSTRACT FROM AUTHOR]

After a review of pseudopotential models for superlattices, we use the superlattice empirical pseudopotential method to predict the wavelength tuning of type II antimonide lasers. We then compare the predictions with a large set of experimental data on a series of optically pumped lasers operating from 2.2 to 9.2 μm. [ABSTRACT FROM AUTHOR]

We report a comparative study on the performance of three optically pumped, type-II quantum well lasers with differing quantum well (QW) confinement. One of the active regions emphasized hole confinement, another emphasized electron confinement, while the third incorporated both electron and hole confinements. In all cases the wells were inserted in a thick InxGa1-xAsySb1-y waveguide/absorber region. The lasing wavelengths at 84 K were 2.26, 3.44, and 2.37 μm, respectively. The maximum peak output powers and differential quantum efficiencies η at 84 K were similar for the hole well and W lasers (≈13 W,η≈0.55), but significantly reduced in the electron-well-only laser (2.3 W,η=0.14). Waveguide loss measurements via the traditional quantum efficiency versus cavity length method and by a Hakki-Paoli method revealed that all three lasers had low waveguide loss that either increased slowly or not at all with increasing temperature. However, the laser’s internal efficiency, ηi, showed a linear decline with increasing temperature, with the ηi of the electron-well-only laser significantly less than the other two. The data suggest that for antimonide-based type-II designs, strong hole confinement is essential for improved performance. The data further suggest that it is hole leakage from the QW and/or hole dilution that is largely responsible for the degradation in laser performance. [ABSTRACT FROM AUTHOR]

We report on measurements of the temperature dependence of the gain and internal waveguide loss of a 3.4 μm, optically pumped InAs/InGaSb, type II, W laser. A high-resolution Fourier transform infrared spectrometer was used to measure the laser mode spectra below threshold. To obtain an accurate determination of the gain, a full-curve fit to the spectral output of the Fabry–Pérot cavity was utilized. Our results indicate very low waveguide loss (a≈3 cm[sup -1]) at 78 K, with no apparent increase up to at least 120 K. Additional measurements of the gain properties of the device reveal a rapidly decreasing differential gain (dG/dP) and a rapidly increasing transparency pump power with increasing temperature. Moreover, measurements of the peak gain at constant pumping show a rapid decline with increasing temperature. Theoretical superlattice-empiricalpseudopotential-model-based calculations suggest that the substantial differences between the conduction and valence subband in-plane curvatures contribute to the rapid decline in gain with increasing temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a rationalized biquadratic interpolation algorithm for calculating quaternary semiconductor parameters and apply it to determine the band gaps of AlGaInAs, AlGaInP, AlInAsSb, GaInPAs, and GaInAsSb over complete compositional ranges. Extension to include bicubic corrections and quinary alloys are discussed. The band gaps of lattice-matched AlGaInAsSb and AlGaInPAs are reported. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have grown single-quantum wells of strained Ga[sub 1 - x]In[sub x]Sb (x<0.35) embedded in GaSb by molecular-beam epitaxy to investigate the photoluminescence and the band offset of this heterojunction. The photoluminescence shifts to longer wavelengths when the well thickness, or the indium content x, is increased. The band offsets of these heterojunctions are estimated by fitting the photoluminescence data to a single-quantum well model. Our offset estimates support the theoretical prediction by first-principles calculations for these strained heterojunctions. [ABSTRACT FROM AUTHOR]

In this article, we report on a systematic study of mid-IR, W-Integrated Absorber (W-IA), lasers that employ strained InAs/In[SUBx]Ga[SUB1-x]Sb/InAs active layers, in which the indium content of the hole bearing In[SUBx]Ga[SUB1-x]Sb has been varied from x[SUPIn] = 0 to x[SUPIn] = 0.45. The output characteristics of the lasers improve as the In percentage is increased; the threshold temperature sensitivity (T[SUB0] values are observed to increase from ≈35 to ≈50 K. Further, the differential quantum efficiencies as a function of temperature are significantly improved in the devices with X[SUPIn] &ges; 0.25. For samples with nominally eight monolayers (8 ML) InAs/7 ML In[SUBx]Ga[SUB1-x]Sb/8 ML InAs, the lasing wavelength at 84 K is observed to shift from 3.33 μm for x[SUPIn] = 0 out to a maximum of 4.62 μm for x[SUPIn] = 0.35. This large shift is well predicted by an empirical psuedopotential model; the model also predicts that the position of the hole wave function is sensitively dependent on strain level and that for x[SUPIn] < 0.25, the holes are no longer confined in the W active region, but rather in the thick IA layers where they experience a bulklike density of states. This suggests that the improved thermal performance with increasing strain is due to the onset of hole quantum confinement in the W region, and improved or deeper hole confinement in that epitaxial layer. [ABSTRACT FROM AUTHOR]

We describe the photoluminescence spectroscopy (PL) and Fourier transform infrared absorbance spectroscopy characterization of a large set of InAs/GaSb type-II strained layer superlattice (SLS) samples. The samples are designed to probe the effect of GaSb layer thickness on the optical properties of the SLS, while the InAs-layer thickness is held fixed. As the GaSb layer thickness is increased, we observe a spectral blue shift of the PL peaks that is accompanied by an increase in intensity, narrower linewidths, and a large reduction in the temperature sensitivity of the luminescence. These effects occur despite a significant reduction in the electron-hole wave function overlap as the GaSb layer thickness is increased. In addition, we compare the results of empirical pseudopotential model (EPM) calculations to the observed blueshift of the primary band gap. The EPM calculations are found to be in very good agreement with the observed data. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A comparative study on the performance of three optically pumped, type-ll quantum well lasers with different quantum well (QW) confinement was reported. Waveguide loss measurements via the traditional quantum efficiency versus cavity length method and by a Hakki-Paoli revealed that all three lasers had low waveguide loss that either increased slowly or not at all with increasing temperature and the data suggest that for antimonide-based type-ll design strong hole confinement is essential for improved performance.

A systematic study of mid-IR, W-Integrated Absorber (W-IA), lasers that employ strained InAs/In(sub x)Ga(sub 1-x)Sb/InAs activelayers, in which the indium content of the hole bearing In(sub x)Ga(sub 1-x)Sb has been varied from x(super In)=0 to x(super In)=0.45, is presented. The result suggests that the improved thermal performance with increasing strain is due to the onset of hole quantum confinement in the W region, and improved or deeper hole confinement in that epitaxial layer.

Examines the alloy structure and properties of InGaAsSb on Indium phosphide. Significance of the use of very-low energy ion irradiation; Effects of low-energy ion irradiation on the growth of alloys; Composition modulations present in alloys grown within a miscibility gap.