InAs/AlSb double-barrier structure with large peak-to-valleycurrent ratio: a candidate for high-frequency microwave devices

Negative differential resistance (NDR) in InAs/AlSb/InAs/AlSb/InAs double-barrier structures with peak-to-valley current (PVC) ratios as large as 11 at room temperature and 28 at 77 K is reported. This is a large improvement over previous results for these materials and is also considerably better than those obtained for the extensively studied GaAs/AlGaAs material system. The peak current density was also improved by reducing the barrier thickness, and values exceeding 10⁵ A/cm² have been observed. These results suggest that InAs/AlSb structures are interesting alternatives to conventional GaAs/AlGaAs structures in high-frequency devices. NDR in a InAs/AlSb superlattice double-barrier structure with a lower PVC ratio than in the solid barrier case has also been observed. This result indicates that valley current contributions arising from X-point tunneling are negligible in these structures, consistent with the large band offset     

Investigation of the influence of the well and the barrierthicknesses in GaSb/AlSb/GaSb/AlSb/InAs double-barrier interbandtunneling structures

The tunneling currents of GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling (DBIT) structures were studied experimentally by varying the thickness of the well and the barrier layers systematically. The optimal thicknesses for the GaSb well and the AlSb barriers were found to be 6.5 and 1.0 nm, respectively, to obtain a high peak current density (19 kA/cm²), with a large peak-to-valley ratio of 4. The high peak current in the DBIT structure shows the strong effect of the resonant coherence of the wave function across the double barrier. For the case of a small GaSb well width (3 nm), a drastic reduction of the peak current was observed, an effect suggesting that the electron-wave function in the InAs couples primarily to the quantized light hole state in the GaSb well     

1.54 lm GaSb/AlGaSb multi-quantum-well monolithic laser at 77 K grown on miscut Si substrate using interfacial misfit arrays

A GaSb quantum-well (QW) laser diode grown monolithically on a 5deg miscut Si (001) substrate is presented. The III-Sb epi-structure is grown monolithically on the miscut Si substrate via a thin (50 nm) AlSb nucleation layer. The 13% lattice mismatch between AlSb and Si is accommodated by a self-assembled 2D array of interfacial misfit dislocations (IMF). The 5deg miscut geometry enables simultaneous IMF formation and anti-phase domain suppression. The 1 mm times 100 mum GaSb QW laser diode operates under pulsed conditions at 77 K with a threshold current density of 2 kA/cm² and a maximum peak power of ~20 mW. Furthermore, the device is characterised by a 9.1 Omega forward resistance and a leakage current density of 0.7 A/cm² at -5 V.     

Low-threshold injectorless quantum cascade laser with four material compositions

A new design for an injectorless quantum cascade laser resulting in a threshold current density of 0.57 kA/cm² at 300 K and a maximum operation temperature of 360 K is presented. The active zone is realised in the strain compensated material system Al(In)As-(Ga)InAs using AlAs barriers for increasing the T₀ and InAs for strain compensation. Additionally the laser performance was improved compared to previous work.     

High-transconductance InAs/AlSb heterojunction field-effecttransistors with δ-doped AlSb upper barriers

The authors report the fabrication and temperature-dependent characterization of InAs/AlSb quantum-well heterojunction field-effect transistors (HFETs). Devices with electron sheet concentrations of 3.8×10¹² cm^-2 and low-field electron mobilities of 21000 cm²/V-s have been realized through the use of Te δ-doping sheets in the upper AlSb barrier. One device with a 2.0-μm gate length showed a peak extrinsic transconductance of 473 mS/mm at room temperature. Gate leakage current, operating current density, and extrinsic transconductance were found to decrease with decreasing temperature     

1.7-ps, microwave, integrated-circuit-compatible InAs/AlSb resonanttunneling diodes

Microwave integrated-circuit-compatible InAs/AlSb resonant tunneling diodes (RTDs) have been fabricated. The resulting devices have peak current densities of 3.3×10⁵ A/cm² with peak-to-valley ratios of 3.3. Switching transition times of 1.7 ps are measured using electrooptic sampling techniques     

The performances of (InAs)1/(GaAs)2short-period superlattice strained single-quantum-well laser on GaAssubstrate

We fabricated an (InAs)₁/(GaAs)₂ short-period superlattice (SPS) strained quantum-well laser at 1.07 μm by MOVPE. The SPS active layer has 10 periods of (InAs)₁/(_GaAs)₂ and an average mismatch of over 2.2%. In highly strained conditions the device showed a lasing wavelength of 1.07 μm, a threshold of 130 A/cm², and a characteristic temperature T₀ of 175 K. We measured the gain characteristic by the Hakki and Paoli method at LED conditions and obtained a high differential gain of 2.0×10^-15 cm² at the threshold current     

p-channel modulation-doped field-effect transistors based on AlSb0.9As0.1/GaSb

Operation of the first AlSbAs/GaSb p-channel modulation-doped field-effect transistor (MODFET) is reported. Devices with 1-μm gate length exhibit transconductance of 30 and 110 mS/mm at room temperature and 80 K, with respective maximum drain current densities of 25 and 80 mA/mm. The low field Hall mobility and sheet carrier density of this modulation doped structure were 260 cm²/V-s and 1.8×10 ¹² cm^-2 at room temperature and 1700 cm²/V-s and 1.4×10¹² cm^-2 at 77 K. Calculations based on these results indicate that room-temperature transconductances of 200 mS/mm or greater could be achieved. This device can be integrated with an InAs n-channel HFET for complementary circuit applications     

Gain measurements on GaAs-based quantum cascade lasers using atwo-section cavity technique

A two-section cavity device has been used to measure gain spectra and waveguide losses of a GaAs-based quantum cascade laser. The device operates at 8.9 μm and optical confinement is obtained by means of Al-free cladding layers. We investigated the gain characteristics in a spectral window of ~60 meV and up to 200 K. For current densities ranging from 1 to 8 kA/cm², we report a constant gain coefficient of 13 cm/kA at 4 K and 6 cm/kA at 200 K. At low temperatures and for current densities above 8 kA/cm², we observe gain saturation which we attribute to a reduced electron injection in the active region caused by space charge effects. We report a value of 22 cm ^-1 for the waveguide losses in good agreement with previous measurements     

Quantum cascade laser utilising aluminium-free material system: InGaAs/GaAsSb lattice-matched to InP

The demonstration of an aluminium-free quantum cascade laser is reported. The presented quantum cascade laser has been realised in an InGaAs/GaAsSb material system lattice-matched to InP. Laser emission is observed at a wavelength around 11.3 mum. The threshold current density is 1.7 kA/cm² at 78 K, and a maximum optical output power of 20 mW at the same temperature is reported.     

InAs/AlSb/GaSb resonant interband tunneling diodes andAu-on-InAs/AlSb-superlattice Schottky diodes for logic circuits

Integrated resonant interband tunneling (RIT) and Schottky diode structures, based on the InAs/GaSb/AlSb heterostructure system, are demonstrated for the first time. The RIT diodes are advantageous for logic circuits due to the relatively low bias voltages (~100 mV) required to attain peak current densities in the mid-10⁴ A/cm ² range. The use of n-type InAs/AlSb superlattices for the semiconducting side of Schottky barrier devices provides a means for tailoring the barrier height for a given circuit architecture. The monolithically integrated RIT/Schottky structure is suitable for fabrication of a complete diode logic family (AND, OR, XOR, INV)     

InAs/AlSb quantum cascade lasers operating at 6.7 /spl mu/m

Quantum cascade lasers based on the InAs/AlSb material system have been realised. The optical confinement is obtained using a plasmon waveguide with n/sup +/-InAs cladding layers. In pulse mode the lasers emit close to 6.7 /spl mu/m with a threshold current density of 5 kA/cm/sup 2/ at 90 K. The maximum operating temperature is 220 K.     

Short-Injector Quantum Cascade Laser Emitting at 8-$mu$m Wavelength With High Slope Efficiency

This letter presents experimental results of a three-alloy-based short-injector quantum cascade laser (QCL). The investigated 4-mm-long device shows a pulsed threshold current density of 1.24 kA/cm² , a slope efficiency of 1.4 W/A, a characteristic temperature above 250 K, and a peak average output power above 726 mW at room temperature. A good high-temperature performance is attributed to the diagonal transition design and better depopulation of the lower laser levels at higher temperatures. The laser emission wavelength at room temperature is 8 mum, resulting in a low voltage defect of 71 meV per period for the QCL structure.     

InP-In1-xGaxAsyP1-yembedded mesa stripe lasers

A laser structure was fabricated using two-step liquid-phase epitaxy, employing the melt-back technique. The fabrication and properties of this structure are described in detail. Good linearity of the power output up to power levels of 20 mW was obtained. The threshold current density at 300 K is 9-12 kA/cm². This high value is mainly due to Zn-diffusion from the third to the buffer layer during the second growth step of the fabrication process. The external differential quantum efficiency is 30-35 percent under pulsed operation at 25°C. The pulsed threshold current has an exponential behavior with temperature whereT_{0} = 60degC. The far-field beam divergences in the directions parallel and perpendicular to the junction plane are12-15degand35-40deg, respectively. Transverse mode stabilization was improved with this laser structure.     

Low-threshold room-temperature operation of injectorless quantum-cascade lasers: influence of doping density

The influence of the doping density in the active sections of InP-based injectorless quantum cascade lasers, emitting at 6.8 mum, is investigated. The doping sheet density is varied in the range 2.5-8.6times10¹⁰ cm^-2. Lasing is observed in the whole range, with a threshold current density as low as 1.2 kA/cm² at 300 K for the smallest doping sheet density of 2.5times10 ¹⁰ cm^-2. Further improvement has been made by additionally increasing the number of periods in the active region from 40 to 60. With the same doping level of 2.5times10¹⁰ cm^-2 record low threshold current densities of 0.73 kA/cm² at 300 K were achieved     

1.6 µm wavelength GaInAsP/InP lasers prepared by two-phase solution technique

Reduction of the threshold current of GaInAsP lasers with an antimeltback layer was studied in the wavelength range1.50-1.65 mun. The two-phase solution growth technique was applied using a relatively low temperature and a slow cooling rate of 0.17°C/min to reduce the active layer thickness. The antimeltback layer with a bandgap wavelength of 1.35 μm resulted in a flat active layer and eliminated the melt-back problem completely. From experiments and calculations we found that both the carrier and the optical confinement of this structure, having an antimeltback layer, were almost the same as those for the conventional InP cladding structure. A threshold eurrent density as low as 1.2 kA/cm²and an active layer thickness of 0.20μm were obtained at these wavelengths. The lattice-match condition of low-temperature growth was studied. In the low-temperature growth, the longer wavelength lasers were grown with the same amount of InAs.J_{th}/dwas independent of the growth condition (T_{S}, T_{G}) and had a value of 5-6 kA/cm². μm.     

Be-implanted GaInAsP/InP double heterojunction laser diodes

Beryllium ion implantation has been used to fabricate broad-area GaInAsP/InP laser diodes operating at a wavelength of 1.3 μm, which have threshold current densities comparable to those obtained using conventional Zn doping during the epitaxial growth process. Both a Be-implant schedule which results in minimal diffusion of the implanted Be and one which results in significant diffusion have been investigated. On most wafers, the average normalized threshold current density (J_{nom} = J_{th}/d) using either implant schedule has been typically 6-8 kA/cm². μm. The lowest Jnomobserved was 4.2 kA/cm². μm and was measured on a "nondiffused" implanted laser.     

High-operating-temperature MWIR photodetector based on a InAs/GaSb superlattice grown by MOCVD

We demonstrate a high-operating-temperature(HOT)mid-wavelength InAs/GaSb superlattice heterojunction in-frared photodetector grown by metal-organic chemical vapor deposition.High crystalline quality and the near-zero lattice mis-match of a InAs/GaSb superlattice on an InAs substrate were evidenced by high-resolution X-ray diffraction.At a bias voltage of-0.1 V and an operating temperature of 200 K,the device exhibited a 50%cutoff wavelength of~4.9μm,a dark current dens-ity of 0.012 A/cm²,and a peak specific detectivity of 2.3×10⁹ cm·Hz^1/2/W.     

Demonstration of 3.5 μm Ga1-xInxSb/InAssuperlattice diode laser

A demonstration of a semiconductor diode laser based on a type-II Ga _1-xIn_xSb/InAs superlattice active layer is reported. The laser structure uses InAs/AlSb superlattice cladding layers and a multiquantum well active layer with GaInAsSb barriers and Ga_1-xIn_xSb/InAs-superlattice wells. An emission wavelength of 3.47 μm for pulsed operation up to 160 K is observed     

Impact ionization suppression by quantum confinement: Effects onthe DC and microwave performance of narrow-gap channel InAs/AlSb HFET's

InAs/AlSb heterostructure field-effect transistors (HFET's) are subject to impact ionization induced short-channel effects because of the narrow InAs channel energy gap. In principle, the effective energy gap to overcome for impact ionization can be increased by quantum confinement (channel quantization) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of quantum well thickness on the dc and microwave performance of narrow-gap InAs/AlSb HFET's fabricated on nominally identical epitaxial layers which differ only by their quantum well thickness. We show that a thinner quantum well postpones the onset of impact ionization and suppresses short-channel effects. As expected, the output conductance g_DS and the gate leakage current are reduced. The f_MAX/f_T ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 Å. The use of the thinner well reduces the cutoff frequency f_T, the transconductance g_m, and the current drive because of the reduced low-field mobility due to interface roughness scattering in thin InAs/AlSb channel layers: the low-field mobility was μ=21 000 and 9000 cm²/Vs for the 100- and 50-Å quantum wells, respectively. To our knowledge, the present work is the first study of the link between channel quantization, in-plane impact ionization, and device performance in narrow-gap channel HFET's