We report on the substantial advancement of long wavelength InAs-based interband cascade lasers (ICLs) utilizing advanced waveguides formed from hybrid cladding layers and targeting the 10-12μm wavelength region. Modifications in the hole injector have improved carrier transport in these ICLs, resulting in significantly reduced threshold voltages (Vth) as low as 3.62 V at 80 K. Consequently, much higher voltage efficiencies were observed, peaking at about 73% at 10.3μm and allowing for large output powers of more than 100 mW/facet. Also, low threshold current densities (Jth) of 8.8 A/cm2 in cw mode and 7.6 A/cm2 in pulsed mode near 10μm were observed; a result of adjustments in the GaInSb hole well composition intended to reduce the overall strain accumulation in the ICL. Furthermore, an ICL from the second wafer operating at a longer wavelength achieved a peak voltage efficiency of 57% at 11.7μm, with a peak output power of more than 27 mW/facet. This ICL went on to lase beyond 12μm in both cw and pulsed modes, representing a new milestone in long wavelength coverage for ICLs with the standard W-QW active region.
Photocathodes based on GaAs and other III-V semiconductors are capable of producing highly spin-polarized electron beams. GaAs/GaAsP superlattice photocathodes exhibit high spin polarization; however, the quantum efficiency (QE) is limited to 1% or less. To increase the QE, we fabricated a GaAs/GaAsP superlattice photocathode with a Distributed Bragg Reflector (DBR) underneath. This configuration creates a Fabry-Pérot cavity between the DBR and GaAs surface, which enhances the absorption of incident light and, consequently, the QE. These photocathode structures were grown using molecular beam epitaxy and achieved record quantum efficiencies exceeding 15% and electron spin polarization of about 75% when illuminated with near-bandgap photon energies.
We report significantly enhanced device performance in long wavelength interband cascade lasers (ICLs) by employing a recently proposed innovative quantum well (QW) active region containing strained InAsP layers. These ICLs were able to operate at wavelengths near 14.4 μm, the longest ever demonstrated for III-V interband lasers, implying great potential of ICLs to cover an even wider wavelength range. Also, by applying the aforesaid QW active region configuration on ICLs at relatively short wavelengths, ICLs were demonstrated at a low threshold current density (e.g., 13 A/cm2 at 80 K) and at temperatures up to 212 K near 12.4 μm, more than 50 K higher than the previously reported ICLs with the standard W-shape QW active region at similar wavelengths. This suggests that the QW active region with InAsP layers can be used to improve device performance at the shorter wavelengths.
We report on a two-step technique for post-bond III-V substrate removal involving precision mechanical milling and selective chemical etching. We show results on GaAs, GaSb, InP, and InAs substrates and from mm-scale chips to wafers.
We report on a two-step technique for post-bond III-V substrate removal involving precision mechanical milling and selective chemical etching. We show results on GaAs, GaSb, InP, and InAs substrates and from mm-scale chips to wafers.
InAs-based interband cascade lasers (ICLs) can be more easily adapted toward long wavelength operation than their GaSb counterparts. Devices made from two recent ICL wafers with an advanced waveguide structure are reported, which demonstrate improved device performance in terms of reduced threshold current densities for ICLs near 11 μm or extended operating wavelength beyond 13 μm. The ICLs near 11 μm yielded a significantly reduced continuous wave (cw) lasing threshold of 23 A/cm2 at 80 K with substantially increased cw output power, compared with previously reported ICLs at similar wavelengths. ICLs made from the second wafer incorporated an innovative quantum well active region, comprised of InAsP layers, and lased in the pulsed-mode up to 120 K at 13.2 μm, which is the longest wavelength achieved for III-V interband lasers.
Proceedings of SPIE - The International Society for Optical Engineering
Fredricksen, C.J.; Peale, R.E.; Dhakal, N.; Barrett, C.L.; Boykin II, O.; Maukonen, D.; Davis, L.; Ferarri, B.; Chernyak, L.; Zeidan, O.A.; Hawkins, Samuel D.; Klem, John F.; Krishna, Sanjay; Kazemi, Alireza; Schuler-Sandy, Ted
Effects of gamma and proton irradiation, and of forward bias minority carrier injection, on minority carrier diffusion and photoresponse were investigated for long-wave (LW) and mid-wave (MW) infrared detectors with engineered majoritycarrier barriers. The LWIR detector was a type-II GaSb/InAs strained-layer superlattice pBiBn structure. The MWIR detector was a InAsSb/AlAsSb nBp structure without superlattices. Room temperature gamma irradiations degraded the minority carrier diffusion length of the LWIR structure, and minority carrier injections caused dramatic improvements, though there was little effect from either treatment on photoresponse. For the MWIR detector, effects of room temperature gamma irradiation and injection on minority carrier diffusion and photoresponse were negligible. Subsequently, both types of detectors were subjected to gamma irradiation at 77 K. In-situ photoresponse was unchanged for the LWIR detectors, while that for the MWIR ones decreased 19% after cumulative dose of ~500 krad(Si). Minority carrier injection had no effect on photoresponse for either. The LWIR detector was then subjected to 4 Mrad(Si) of 30 MeV proton irradiation at 77 K, and showed a 35% decrease in photoresponse, but again no effect from forward bias injection. These results suggest that photoresponse of the LWIR detectors is not limited by minority carrier diffusion.
We discuss thinned InAsSb resonant infrared detectors that are designed to enable high quantum efficiency by using interleaved nanoantennas to read out two wavelengths from each pixel simultaneously.
Carrasco, Rigo A.; Morath, Christian P.; Grant, Perry C.; Ariyawansa, Gamini; Reyner, C.J.; Stephenson, Chad A.; Kadlec, Clark N.; Hawkins, Samuel D.; Klem, John F.; Steenbergen, Elizabeth H.; Schaefer, Stephen T.; Johnson, Shane R.; Zollner, S.; Webster, Preston T.
Gallium is incorporated into the strain-balanced In(Ga)As/InAsSb superlattice system to achieve the same mid-wave infrared cutoff tunability as conventional Ga-free InAs/InAsSb type-II superlattices, but with an additional degree of design freedom to enable optimization of absorption and transport properties. Time-resolved photoluminescence measurements of InGaAs/InAsSb superlattice characterization- and doped device structures are reported from 77 to 300 K and compared to InAs/InAsSb. The low-injection photoluminescence decay yields the minority carrier lifetime, which is analyzed with a recombination rate model, enabling the determination of the temperature-dependent Shockley-Read-Hall, radiative, and Auger recombination lifetimes and extraction of defect energy levels and capture cross section defect concentration products. The Shockley-Read-Hall-limited lifetime of undoped InGaAs/InAsSb is marginally reduced from 2.3 to 1.4 μs due to the inclusion of Ga; however, given that Ga improves the vertical hole mobility by a factor of >10×, a diffusion-limited InGaAs/InAsSb superlattice nBn could expect a lower bound of 2.5× improvement in diffusion length with significant impact on photodetector quantum efficiency and radiation hardness. At temperatures below 120 K, the doped device structures are Shockley-Read-Hall limited at 0.5 μs, which shows promise for detector applications.
We have fabricated and characterized AlInAsSb- and InPAsSb-absorber nBn infrared detectors with 200 K cutoff wavelengths from 2.55 to 3.25 μm. Minority-carrier lifetimes determined by microwave reflectance measurements were 0.2-1.0 μs in doped n-type absorber materials. Devices having 4 μm thick absorbers exhibited sharp cutoff at wavelengths of 2.9 μm or longer and softer cutoff at shorter wavelengths. Top-illuminated devices with n+ InAs window/contact layers had external quantum efficiencies of 40-50% without anti-reflection coating at 50 mV reverse bias and wavelengths slightly shorter than cutoff. Despite the shallow-etch mesa nBn design, perimeter currents contributed significantly to the 200 K dark current. Dark currents for InPAsSb devices were lower than AlInAsSb devices with similar cutoff wavelengths. For unoptimized InPAsSb devices with 2.55 μm cutoff, 200 K areal and perimeter dark current densities at -0.2 V bias in devices of various sizes were approximately 1x10-7 A/cm2 and 1.4x10-8 A/cm, respectively.
Here, the design, fabrication, and characterization of an actively tunable long-wave infrared detector, made possible through direct integration of a graphene-enabled metasurface with a conventional type-II superlattice infrared detector, are reported. This structure allows for post-fabrication tuning of the detector spectral response through voltage-induced modification of the carrier density within graphene and, therefore, its plasmonic response. These changes modify the transmittance through the metasurface, which is fabricated monolithically atop the detector, allowing for spectral control of light reaching the detector. Importantly, this structure provides a fabrication-controlled alignment of the metasurface filter to the detector pixel and is entirely solid-state. Using single pixel devices, relative changes in the spectral response exceeding 8% have been realized. These proof-of-concept devices present a path toward solid-state hyperspectral imaging with independent pixel-to-pixel spectral control through a voltage-actuated dynamic response.
We report here our recent electron transport results in spatially separated two-dimensional electron and hole gases with nominally degenerate energy subbands, realized in an InAs(10 nm)/GaSb(5 nm) coupled quantum well. We observe a narrow and intense maximum (∼500 kΩ) in the four-terminal resistivity in the charge neutrality region, separating the electron-like and hole-like regimes, with a strong activated temperature dependence above T = 7 K and perfect stability against quantizing magnetic fields. We discuss several mechanisms for that unexpectedly large resistance in this zero-gap semi-metal system including the formation of an excitonic insulator state.