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We employ a cavity-length study to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269K with an emission wavelength of 4.05μm. The characteristic temperature for the gain per unit current density is 39K, which is slightly lower than T0 of the threshold current and is consistent with dominance by Auger recombination. The internal loss for the 150-μm-wide mesa devices increased from 11cm−1 at 78Kto28cm−1 at 275K.

Two ten-stage interband cascade laser structures were grown by solid-source molecular beam epitaxy. The wafers were processed into both broad-area ridges for threshold characterization and Au-electroplated narrow ridges for high-temperature cw operation. Pulsed threshold current densities in the broad-area devices were as low as 3.8 A/cm2 at 78 K and 590 A/cm2 at 300 K. An 11-μm-wide ridge exhibited a new maximum cw operating temperature of 288 K at λ=4.1 μm. An even longer-wavelength device emitted at 5.1 μm with a maximum cw operating temperature of 229 K.

The authors report the fabrication and characterization of mid-IR HgCdTe negative luminescence (NL) devices grown on silicon substrates. Sensitive optical modulation measurements of the 5mm square array with ∼5.4μm cutoff and single-layer antireflection (AR) coating yield an internal NL efficiency of 98% at room temperature. This is the highest ever reported, and represents a factor-of-50 suppression of the blackbody emission. The corresponding external NL efficiency of 86% is consistent with the internal efficiency and the spectrally weighted reflectivity of 15%, which could be improved substantially through the incorporation of a state-of-the-art multilayer AR coating.

We studied the low-temperature magnetotransport properties of AlxGa1−xN∕AlN∕GaN heterostructures with a two-dimensional electron gas (2DEG). Structures with different Al compositions were grown by metal-organic vapor-phase epitaxy on three types of templates: conventional undoped GaN, in situ epitaxial lateral overgrown GaN using a SiNx nanomask layer, and ex situ epitaxial lateral overgrown GaN (ELO-GaN) using a stripe-patterned SiO2 mask. All of the samples display Shubnikov–de Haas (SdH) oscillations that confirm the existence of 2DEGs. Field-dependent magnetoresistance and Hall measurements further indicate that the overgrown heterostructures have a parallel conducting layer in addition to the 2DEG. To characterize the parallel channel, we repeated the measurements after the 2DEG was etched away. 2DEG carrier density values were then extracted from the SdH data, whereas the zero-field 2DEG conductivity was determined by subtracting the parallel channel conductivity from the total. The quantitative mob...

The authors report the operating characteristics of ten-stage interband cascade lasers from two wafers with room-temperature wavelengths of 4.1 and 4.3μm. For 150-μm-wide stripes, the threshold current densities are as low as 4.8A∕cm2 at 78K (cw) and 1.15kA∕cm2 at room temperature (pulsed). At 78K, the cw wall-plug efficiency for an 11-μm-wide ridge with 0.5-mm-long cavity and coated facets is 27%, while a 3-mm-long cavity emits a maximum cw power of 200mW. Devices from the two wafers have maximum cw operating temperatures of 261K (λ≈4.0μm) and 243K (λ≈4.2μm).

GaAsSbN∕InP strained layer superlattice (SL) structures have been grown using low-temperature metal organic chemical vapor deposition with N composition varying from 0.6% to 1.6%. High-resolution x-ray diffraction measurements indicate that GaAsSbN∕InP SLs with defect-free layers and abrupt interfaces were achieved. Low-temperature photoluminescence measurements reveal that nitrogen incorporation into the GaAsSbN layers extends the emission wavelength, increases the conduction band offset, and dramatically changes the As∕Sb ratio. In parallel with the experimental efforts, simulation studies using a ten-band k∙p model are carried out to correlate the emission properties of these SL structures with experiment. Photoluminescence measurements indicate an emission wavelength redshift with respect to the simulated values.

A ten-stage interband cascade laser with 13 mum-wide, 4 mm-long ridge waveguide and Au electroplating for improved epitaxial-side-up heatsinking operates CW to a temperature of 269 K, where the emission wavelength is 4.05 mum. Maximum CW output powers are 130 mW at 78 K, 58 mW at 200 K, and 9 mW at 260 K, and the threshold current density at T=260 K is 660 A/cm 2

Interband cascade lasers with ten active stages were grown by molecular beam epitaxy (MBE). Devices emitting near 3.6μm at room temperature operated in pulsed mode to a temperature of 330K. The threshold current densities were the lowest to date for NRL growths, ranging from 9A∕cm2 at 78Kto1.7kA∕cm2 at 300K. The voltage efficiency was ≈94% at 140K, and the pulsed slope efficiency was 121mW∕A at 300K. Antimonide photodetectors with a cutoff wavelength of 12μm were also grown in the same machine by MBE. The absorbing layer consisted of an InAs∕GaInSb type-II superlattice, and the depletion region comprised a four-layer “W” structure with a graded energy gap in order to minimize the tunneling and generation currents. Quantum efficiencies of 30%–40% were achieved in the 8–10μm band.

A five-stage interband cascade laser with 12μm ridge width and Au electroplating for improved epitaxial-side-up heat sinking operates cw to a maximum temperature of 257K, where the emission wavelength is 3.7μm. The device emits 100mW/facet for cw operation at 80K, 54mW at 200K, and 10mW at 250K. The beam quality is within twice the diffraction limit for injection currents up to 14 times the lasing threshold at 120K.

A new W-structured type-II superlattice photodiode design, with graded band gap in the depletion region, is shown to strongly suppress dark currents due to tunneling and generation-recombination processes. The long-wave infrared (LWIR) devices display 19%–29% quantum efficiency and substantially reduced dark currents. The median dynamic impedance-area product of 216Ωcm2 for 33 devices with 10.5μm cutoff at 78K is comparable to that for state-of-the-art HgCdTe-based photodiodes. The sidewall resistivity of ≈70kΩcm for untreated mesas is also considerably higher than previous reports for passivated or unpassivated type-II LWIR photodiodes, apparently indicating self-passivation by the graded band gap.

The spectral properties and other performance characteristics of single-photon quantum-dot terahertz detectors incorporating single-electron transistors are analyzed for the cases of GaAs and InAs electron channels. By defining the electrostatically confined double-quantum-dot structures in shallow two-dimensional electron gas structures, these devices have the potential to operate at temperatures above the dilution refrigerator range. We calculate the interlevel plasmon absorption by using the random-phase approximation in conjunction with realistic band structures and three-dimensional confinement geometries. While the level separations increase with decreasing dot diameter, carrier depletion eventually limits the minimum size that is viable. The maximum detection frequency is about 1THz for GaAs channels, but increases to 1.5–2THz for InAs channels having a lower effective mass.

Results are presented for an enhanced type-II W-structured superlattice (WSL) photodiode with an 11.3μm cutoff and 34% external quantum efficiency (at 8.6μm) operating at 80K. The new WSL design employs quaternary Al0.4Ga0.49In0.11Sb barrier layers to improve collection efficiency by increasing minority-carrier mobility. By fitting the quantum efficiencies of a series of p-i-n WSL photodiodes with background-doped i-region thicknesses varying from 1to4μm, the authors determine that the minority-carrier electron diffusion length is 3.5μm. The structures were grown on semitransparent n-GaSb substrates that contributed a 35%–55% gain in quantum efficiency from multiple internal reflections.

We demonstrate a surface-emitting photonic-crystal distributed-feedback laser, emitting at λ≈3.7μm from an antimonide type-II “W” active region. While single-mode operation was not achieved, the spectral emission linewidth for cw optical pumping was only 1.3A. For pulsed operation with a pump-spot diameter of 0.8mm, 60% of the nearly circular output beam was transmitted through an aperture with an angular diameter approximately five times that of a Gaussian emitted beam, assuming that the emission area and pump area are the same.

Continuous-wave single-mode emission near λ=3.42μm is obtained from a distributed-feedback (DFB) interband cascade laser. The low-loss DFB mode in the 15-μm-wide ridge is resonant with the gain peak at 110K, where the maximum single-mode output power is 3mW. The instrument-limited linewidth is ⩽0.5A, and the wavelength is linearly tunable over a 4nm range by varying the temperature from 110to125K (0.28nm∕K), or over 0.6nm by varying the current from 60to83mA (0.031nm∕mA).

A ten-stage interband cascade laser emitting at 3.3–3.6μm exhibits a voltage drop only 4% above the theoretical minimum, and operates to room temperature in pulsed mode. At 78K, a five-stage device mounted epitaxial-side-up with coated facets has a maximum cw wallplug efficiency of 21%, and a second device produces up to 1.1W of cw power.

Low temperature (30K) long wavelength photoluminescence emission (λ=1400–1600nm) from metalorganic chemical vapor deposition grown InGaAsN–GaAsSb type II “W” quantum wells (QWs), on GaAs substrates has been demonstrated. Thin layers (2–3nm) and high antimony-content (30%) GaAsSb were utilized in this study for realizing satisfactory wave function overlap and long wavelength emission. Tensile strained GaAsP barriers effectively improve the material structural and luminescence properties of the compressive strained active region. Room temperature photoluminescence data show that the type-II QW design is a promising candidate for realizing long wavelength GaAs-based diode lasers beyond 1500nm.

A five-stage interband cascade laser with ridge width 22 µm and Au electro-plating for improved epitaxial-side-up heatsinking emits >260 mW per facet for CW operation at 80 K (λ=3.4 µm) and 100 mW at 200 K (λ=3.6 µm). The maximum CW operating temperature is 250 K, and the beam quality for a sister device without Au electro-plating is 1.5–3.8 times the diffraction limit.

We studied the I-V characteristics, lasing thresholds, and wall plug efficiencies of type-II “W” mid-IR diode lasers from 16 different wafers. At T=90K, the wall plug efficiency for a 1-mm-long gain-guided device was >10% and the slope efficiency was 142mW∕A (38% external quantum efficiency). When a 22-μm-wide ridge was lithographically defined on a five-period W with ap-GaSb etch stop layer, the maximum cw operating temperature increased to 230K. We also investigated ten-stage interband cascade lasers containing W active quantum wells. While the low-temperature threshold current densities were somewhat higher than in the W diodes, at higher temperatures the pulsed thresholds were slightly lower. The threshold voltage was only ≈0.1V larger than the photon energy multiplied by the number of stages, corresponding to a voltage efficiency of >96%, while the differential series resistance-area product above threshold was as low as 0.21mΩcm2 at 100K. At T=78K, the cw slope efficiency was 0.48mW∕A (126% external...

Pseudomorphic four-period GaAs0.978N0.022∕GaAs0.78Sb0.22 type-II multiquantum well structures were grown on (100) GaAs substrates by metalorganic vapor phase epitaxy at 530°C. The GaAs0.978N0.022 layers were grown at a V/III ratio of 685 and N∕V ratio of 0.96, whereas the GaAs0.78Sb0.22 was grown at a V/III ratio of 3.8 and Sb∕V ratio of 0.8. The superlattice peaks in the x-ray diffraction θ-2θ scans around the (400) GaAs peak were fitted using a dynamical simulation model to determine layer thickness and alloy compositions. The GaAsN and GaAsSb thicknesses were ∼8nm and ∼5nm, respectively. The photoluminescence (PL) spectra were obtained at 30K and the PL peak energy was found to match the type-II transition energy obtained from a 10-band k∙p model. Postgrowth annealing under arsine-H2 with a N2 cooldown was found to increase the low temperature PL intensity and result in the appearance of luminescence at room temperature.

We measured and modeled the performance characteristics of a distributed-feedback quantum-cascade laser exhibiting high-power continuous-wave (CW) operation in a single spectral mode at λ≈4.8μm and temperatures up to 333K. The sidemode suppression ratio exceeds 25dB, and the emission remains robustly single mode at all currents and temperatures tested. CW output powers of 99mW at 298K and 357mW at 200K are obtained at currents well below the thermal rollover point. The slope efficiency and subthreshold amplified spontaneous emission spectra are shown to be consistent with a coupling coefficient of no more than κL≈4–5, which is substantially lower than the estimate of 9 based on the nominal grating fabrication parameters.

A type-II “W” diode laser with five quantum well periods and emitting at λ≈3.5μm operated in cw mode to T=218K. A second device produced more than 500mW of cw power at 80K. The threshold current density at T=78K was 31A∕cm2, and pulsed operation was observed to 317K. Improvements over previous single-stage devices for this wavelength range may be attributed in part to high growth quality and also to the incorporation of transition regions that smooth discontinuities in the conduction-band profile.

Type II “W” diodes designed for emission at the spectral line of methane (3.31μm) when operated near 80K were grown on a compact 21T RIBER molecular beam epitaxy system. Photoluminescence and cross-sectional scanning tunneling microscopy were used as tools to improve the growth quality of these structures. The diodes exhibited very low lasing thresholds at T=80K (24–40A∕cm2), although further development will be required to enhance the characteristic temperature (T0∼40K) and the maximum operating temperature (∼190K). The lasers had favorable internal losses at all T up to 190K (∼7cm−1), and favorable internal efficiencies at low T (up to 85%). The I–V characteristics of nonlasing test structures were improved substantially by adding n-side “transition” regions that smoothed out abrupt steps in the conduction-band offset.

We explored the evolution of the photoluminescence (PL) properties versus molecular beam epitaxy growth conditions for a series of type II “W” quantum well [InAs/GaInSb/InAs/AlAsSb] structures. The highest PL intensities are obtained when the quantum wells are grown in a temperature range between 487 and 507 °C. Cross-sectional scanning tunneling microscopy was used to explain the temperature evolution of the PL. AlAs clustering within the AlAsSb barrier was observed at low growth temperature. The PL intensity decrease at high temperature was related to In clustering in the GaInSb layer. Laser structures grown at both 425 and 500 °C displayed lower lasing thresholds, lower internal losses, and longer Shockley–Read lifetimes than any similar structures grown previously at NRL. A thicker optical cladding layer of 3.5 μm suppressed mode leakage into the substrate and reduced the internal loss to 2.1 cm−1 at 78 K.

Theoretical modelling indicates that photonic-crystal distributed-feedback (PCDFB) lasers should be capable of providing near-diffraction-limited, spectrally pure sources of midwave-infrared radiation. The authors have studied both 2nd-order and 1st-order optically pumped PCDFB lasers with ‘W’ active regions. Whereas it was not possible to optimise the 2nd-order grating due to the limitations of optical lithography, the 1st-order grating was fabricated using electron-beam lithography with a nearly optimum set of coupling coefficients. The resonant wavelength of the 1st-order grating remained somewhat longer than the gain peak at all temperatures up to the maximum for laser operation. In spite of the substantial detuning, the beam quality improved by a factor of five over angled-grating (α‐DFB) lasers fabricated from similar material, and was slightly better than that for the 2nd-order grating at stripe widths

The negative luminescence (NL) of a midwave-infrared (MWIR) HgCdTe photodiode λco = 5.3 µm at 295 K) was investigated using both a modulated, self-referencing, optical technique and an electrical modulation technique. The internal negative luminescence efficiencies measured using optical modulation were 88% throughout the 3–5 µm spectral region, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction of 53 K at room temperature and 35 K at 240 K when a saturation reverse bias is applied. Efficiencies measured by the electrical modulation technique were consistent with the measured internal efficiencies and the measured reflectivity of the device. The reflectance and emission spectra measured with an FTIR spectrometer were modelled using empirical HgCdTe absorption formulas. The reverse saturation current density of 1.3 A/cm2 is lower than any reported previously in the literature for an NL device with cut-off wavelength beyond 4 µm.

We review the recent progress of electrically injected and optically pumped mid-IR lasers based on antimonide quantum wells with the type II W configuration. W quantum-well diodes have achieved cw operation up to 195 K at lambda = 3.25 mum. Optically pumped devices that employ the diamond pressure bond heat sink have reached 290 K at 3 mum and 210 K at 6 mum. Pulsed power conversion efficiencies of up to 7% at 220 K have been attained by use of an optical pumping injection cavity approach, in which an etalon cavity for the pump beam significantly enhances its absorptance. The angled-grating distributed-feedback configuration has been used to obtain near-diffraction-limited output for an optical pumping stripe width of 50 mum.

With optical pumping, a lead salt vertical-cavity surface-emitting laser has been operated at wavelengths in the 4.50-4.60 mm range at temperatures up to T=289 K. For a 60 /spl mu/m/spl times/90 /spl mu/m pump spot, a device with a PbSe active region and Pb/sub 1-x/Sr/sub x/Se/BaF/sub 2/ quarter-wave mirror stacks was realised which had an unsaturated peak output power of 38 mW at 249 K.

While most previous studies of Hg-based mid-IR lasers have focused on either bulk Hg(1-x)Cd(x)Te alloys or thick (100 A) Hg(1-x)Cd(x)Te quantum wells with relatively large x, we show that much thinner (20-30 A) HgTe binary wells may be engineered to suppress both Auger recombination and intervalence free carrier absorption. On the basis of detailed numerical simulations, we predict 4.3 m cw emission at temperatures up to 220 K for optical pumping and 105 K for diode operation. In pulsed mode, we expect maximum lasing temperatures more than 100 K higher than any prior Hg-based mid-IR result.

The authors propose two novel sources emitting in the mid-IR: type-II and type-I interband cascade lasers, and perform detailed gain calculations. High radiative efficiencies are expected, since the phonon processes which dominate relaxation in the intersub-band quantum cascade laser are effectively eliminated.

Optically-pumped type-II W lasers have exhibited improved high-temperature performance throughout the wavelength range of 2.7 micrometer to 7.3 micrometer. Low duty cycle pumping at 2.1 micrometer yielded maximum operating temperatures as high as 360 K at (lambda) less than or equal to 4 micrometer for 3 devices, with peak output powers exceeding 1.5 W at ambient temperature. Internal losses of 90 cm -1 at 300 K were seen for one device and suppressed Auger recombination coefficients were observed for all three. Pulsed operation at wavelengths as long as 7.3 micrometer was seen in another device which had a maximum operating temperature of 220 K. For 1.064 micrometer optical pumping, the same laser was able to operate in continuous-wave (cw) mode to 130 K. Cw operation was also observed at temperatures as high as 290 K for lambda approximately equals 3.0 micrometer. Maximum cw output powers (per uncoated facet) of 260 mW at (lambda) equals 3.1 micrometer and 50 mW at (lambda) equals 5.4 micrometer were observed at T equals 77 K. With further improvements in the design and growth quality of these W laser structures, it is projected the cw output powers of 0.5 W or more should be achievable at thermoelectric cooler temperatures.