J. R. Chavez

Evidence for hole and electron trapping in plasma deposited ZrO2 thin films

We have observed electron and hole trapping phenomena in thin films of ZrO2 obtained by plasma assisted deposition. Limited thickness dependent measurements suggest that the holes are trapped uniformly through the film while the electrons trap at the ZrO2/Si interface. Relaxation of the trapped holes occurs rapidly after removal of negative stress (∼90% in 15 min), while electron relaxation postpositive stress occurs more slowly (∼10% in 100 min). Cycling between states of positive trapped charge and negative trapped charge by application of the appropriate stressing voltage was observed.

High-temperature performance in ∼4 μm type-II quantum well lasers with increased strain

In this article, we report on a systematic study of mid-IR, W-Integrated Absorber (W-IA), lasers that employ strained InAs/InxGa1−xSb/InAs active layers, in which the indium content of the hole bearing InxGa1−xSb has been varied from xIn=0 to xIn=0.45. The output characteristics of the lasers improve as the In percentage is increased; the threshold temperature sensitivity (T0) 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 xIn⩾0.25. For samples with nominally eight monolayers (8 ML) InAs/7 ML InxGa1−xSb/8 ML InAs, the lasing wavelength at 84 K is observed to shift from 3.33 μm for xIn=0 out to a maximum of 4.62 μm for xIn=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 xIn<0.25, the holes are no longer confined in the W active re...

Performance comparison of optically pumped type-II midinfrared lasers

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 84K were 2.26, 3.44, and 2.37μm, respectively. The maximum peak output powers and differential quantum efficiencies η at 84K were similar for the hole well and W lasers (≈13W,η≈0.55), but significantly reduced in the electron-well-only laser (2.3W,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 increasin...

Gain and loss in an optically pumped mid-infrared laser

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–Perot cavity was utilized. Our results indicate very low waveguide loss (a≈3 cm−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 rap...

High power Nd:YAG spinning disk laser.

We report on a high power Nd:YAG spinning disk laser. The eight cm diameter disk generated 200 W CW output with 323 W of absorbed pump in a near diffraction-limited beam. The power conversion efficiency was 64%. The pulsed result, 5 ms pulses at 10 Hz PRF, was nearly identical to the CW result indicating good thermal management. Rotated at 1200-1800 RPM with He impingement cooling the disk temperature increased by only 17 °C reaching a maximum temperature of ~31 °C. The thermal dissipation per unit of output power was 0.61 watt of heat generated per watt of laser output, which is below the typical range of 0.8-1.1 for 808 nm diode pumped Nd:YAG lasers.

Optically pumped type-II antimonide mid-IR lasers with integrated absorber layers

We report on optically pumped mid-IR semiconductor lasers that are based on type-II wells. A systematic study of the effect of increasing the In-content in the InxGa1-xSb hole-well suggests that improved hole confinement results in improved power conversion efficiency at elevated temperatures that is also accompanied by a reduction in threshold power and a reduction in T0, the characteristics for threshold.

The antiguiding parameter in mid-infrared optically pumped semiconductor lasers

We describe measurements of the antiguiding parameter, α, for several optically pumped semiconductor lasers. The two W lasers, incorporated 14 type-II quantum wells (QWs) and operated at wavelengths of ~3.5 and ~4.5 μm. The lasers displayed low antiguiding factors of ~1.0. We attribute the low αs for the W lasers to the higher QW gain as well as to inhomogeneous broadening induced by the 14 QWs. The differing well widths and the independent optical pumping of the wells, leads to a net gain spectrum that is symmetrical about the gain peak. This symmetry, in turn, leads to small differential index shifts at the gain peak; the result of the small differential index and large differential gain is low antiguiding.