Gain and threshold current in type II In(As)Sb mid-infrared quantum dot lasers

In this work, we improved the performance of mid-infrared type II InSb/InAs quantum dot (QD) laser diodes by incorporating a lattice-matched p-InAsSbP cladding layer. The resulting devices exhibited emission around 3.1 μm and operated up to 120 K in pulsed mode, which is the highest working temperature for this type of QD laser. The modal gain was estimated to be 2.9 cm−1 per QD layer. A large blue shift (~150 nm) was observed in the spontaneous emission spectrum below threshold due to charging effects. Because of the QD size distribution, only a small fraction of QDs achieve threshold at the same injection level at 4 K. Carrier leakage from the waveguide into the cladding layers was found to be the main reason for the high threshold current at higher temperatures

The structural evolution of InN nanorods to microstructures on Si (111) by molecular beam epitaxy

We report the catalyst free growth of wurtzite InN nanorods (NRs) and microislands on bare Si(111) by plasma-assisted molecular beam epitaxy at various temperatures. The morphological evolution from NRs to three dimensional (3D) islands as a function of growth temperature is investigated. A combination of tapered, non-tapered, and pyramidal InN NRs are observed at 490 °C, whereas the InN evolves to faceted microislands with an increase in growth temperature to 540 °C and further developed to indented and smooth hemispherical structures at extremely high temperatures (630 °C). The evolution from NRs to microislands with increase in growth temperature is attributed to the lowering of the surface free energy of the growing crystals with disproportionate growth velocities along different growth fronts. The preferential adsorption of In atoms on the (0001) c-plane and (10-10) m-plane promotes the growth of NRs at relatively low growth temperature and 3D microislands at higher temperatures. The growth rate imbalance along different planes facilitates the development of facets on 3D microislands. A strong correlation between the morphological and structural properties of the 3D films is established. XRD studies reveal that the NRs and the faceted microislands are crystalline, whereas the hemispherical microislands grown at extremely high growth temperature contain In adlayers. Finally, photoluminescent emissions were observed at ∼0.75 eV from the InN NRs

Low bandgap mid-infrared thermophotovoltaic arrays based on InAs

We demonstrate the first low bandgap thermophotovoltaic (TPV) arrays capable of operating with heat sources at temperatures as low as 345 °C, which is the lowest ever reported. The individual array elements are based on narrow band gap InAs/InAs0.61Sb0.13P0.26 photodiode structures. External power conversion efficiency was measured to be ∼3% from a single element at room temperature, using a black body at 950 °C. Both 25-element and 65-element arrays were fabricated and exhibited a TPV response at different source temperatures in the range 345–950 °C suitable for electricity generation from waste heat and other applications

Mid-infrared InAs0.79Sb0.21-based nBn photodetectors with Al0.9Ga0.2As0.1Sb0.9 barrier layers, and comparisons with InAs0.87Sb0.13 p-i-n diodes, both grown on GaAs using interfacial misfit arrays

InAs 0.79Sb0.21-based nBn photodetectors were fabricated on a GaAs substrate, using the interfacial misfit array growth mode. Reductions in the dark current density of more than two orders of magnitude at 300 K and more than six orders of magnitude at 200 K were found, in comparison with an InAs 0.87Sb0.13 p-i-n diode. At −0.5 V applied bias, the dark currents were found to be diffusion limited above 150 K. Background limited infrared photodetection and R0A values in excess of 106 Ωcm2 were observed at 150 K. Spectral response measurements revealed a cut-off wavelength of 5.3 μm at 200 K

Photocapacitance study of type-II GaSb/GaAs quantum ring solar cells

In this study, the density of states associated with the localization of holes in GaSb/GaAs quantum rings are determined by the energy selective charging of the quantum ring distribution. The authors show, using conventional photocapacitance measurements, that the excess charge accumulated within the type-II nanostructures increases with increasing excitation energies for photon energies above 0.9 eV. Optical excitation between the localized hole states and the conduction band is therefore not limited to the Γ(k = 0) point, with pseudo-monochromatic light charging all states lying within the photon energy selected. The energy distribution of the quantum ring states could consequently be accurately related from the excitation dependence of the integrated photocapacitance. The resulting band of localized hole states is shown to be well described by a narrow distribution centered 407 meV above the GaAs valence band maximum

Characterisation of Ga(1-x)In(x)Sb quantum wells (x~0.3) grown on GaAs using AlGaSb interface misfit buffer

GaInSb multiple quantum wells (MQW) grown on GaAs using an AlGaSb interface misfit (IMF) metamorphic buffer layer technique exhibit superior infrared photoluminescence (PL) at room temperature compared with MQW grown directly on GaSb. PL emission was obtained in the range from 1.7 μm (4 K) to 1.9 μm (300 K) from Ga1-xInxSb samples containing five compressively strained QW with In content x~0.3. Structural and optical characterisation confirms that the AlGaSb IMF growth technique is promising for the development of photonic devices operating at extended wavelengths based on GaAs substrates

Mid-infrared resonant cavity light emitting diodes operating at 4.5 μm

We report on a mid-infrared resonant cavity light emitting diode (RCLED) operating at the wavelength of 4.5 μm with narrow spectral linewidth at room temperature. Compared to a reference LED without a resonant cavity our RCLED exhibits (85x) higher peak intensity, (13x) higher integrated output power, (16x) narrower spectral linewidth and (7x) superior temperature stability. The device consists of a one-wavelength thick micro-cavity containing an Al0.12In0.88As/InAs0.85Sb0.15 quantum well active region sandwiched between two high contrast AlAs0.08Sb0.92/GaSb distributed Bragg reflector mirrors, grown lattice–matched on GaSb by molecular beam epitaxy. The high spectral brightness, narrow linewidth and superior temperature stability, are attractive features, enabling these devices to be used for detection of N2O at 4.5 μm. We show that with only minor adjustments the gases CO2 (4.2 μm) and CO (4.6 μm) are also readily accessible

InAsSb-based nBn photodetectors:lattice mismatched growth on GaAs and low-frequency noise performance

An InAsSb nBn detector structure was grown on both GaAs and native GaSb substrates. Temperature dependent dark current, spectral response, specific detectivity (D*) and noise spectral density measurements were then carried out. Shot-noise-limited D*figures of 1.2 10 Jones × 10 and 3.0 10 Jones × 10 were calculated (based upon the sum of dark current and background photocurrent) for the sample grown on GaAs and the sample grown on GaSb, respectively, at 200 K. Noise spectral density measurements revealed knee frequencies of between 124–337 Hz and ∼8 Hz, respectively. Significantly, these devices could support focal plane arrays capable of operating under thermoelectric cooling

Room temperature mid-infrared InAsSbN multi-quantum well photodiodes grown by MBE

Room temperature photoresponse in the mid-infrared spectral region is demonstrated from InAsSbN/InAs multi-quantum well photodiodes grown by nitrogen plasma assisted molecular beam epitaxy. The structural quality of the InAsSbN MQWs was ascertained in-situ by reflection high energy electron diffraction and ex-situ by high resolution X-ray diffraction and photoluminescence measurements. The extended long wavelength photoresponse is identified to originate from the electron-heavy hole (e1-hh1) and electron-light hole (e1-lh1) transitions in the InAsSbN MQW, with a cut off wavelength ~ 4.20 µm and peak detectivity D* =1.25×109 cm Hz1/2 W-1