Joerg Heber

Comparative study of ultrafast intersubband electron scattering times at ∼1.55 μm wavelength in GaN/AlGaN heterostructures

We report on a comparative study of room temperature intersubband electron scattering lifetimes in GaN/AlGaN single and coupled double multiple quantum well (QW) samples with peak absorption wavelengths ranging from 1.4 to 1.7 μm. Using time-resolved pump-probe spectroscopy electron scattering times as short as ∼160 fs have been measured for a coupled QW sample and ≲300 fs for single QW samples. While no significant dependence on the excitation power has been observed, a decrease of the scattering times with increasing probe wavelength has been measured and may be attributed to monolayer fluctuations in the samples.

Materials science: Enter the oxides

Thin films of oxygen-bearing compounds could have myriad practical applications, finds Joerg Heber, if a few problems can be overcome.

Type-II InAs/InAsSb strained-layer-superlattice negative luminescence devices

Negative luminescence operation is reported for p–n diode devices with type-II InAs/InAsSb strained-layer-superlattice active regions which have a spectral peak at 4.2 μm and a negative luminescence efficiency of up to 20%.

Plasmonics: Surfing the wave

Small oscillations of surface electrons that manipulate light on the nanoscale could be the route to applications as disparate as faster computer chips and cures for cancer. Joerg Heber reports.

Room-temperature InAsSb strained-layer superlattice light-emitting diodes at λ=4.2 μm with AlSb barriers for improved carrier confinement

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

Efficient 300 K light-emitting diodes at λ∼5 and ∼8 μm from InAs/In(As1−xSbx) single quantum wells

300 K light-emitting diodes which emit at 5 and 8 μm with quasi-cw output powers of up to 50 and 24 μW, respectively, are reported. The devices have a single molecular beam epitaxy grown InAs/In(As, Sb) quantum well in the active region with a strong type-IIa band alignment giving mid-IR emission at energies up to 64% lower than the alloy band gap. The emission energies are shown to be in good agreement with a k⋅p bandstructure model where Qc, the ratio of the strained conduction-band offset to the band-gap difference between the two strained superlattice components, is found to be ∼2.0.

Recent progress in GaN-based superlattices for near-infrared intersubband transitions

A review of the recent progress in intersubband transitions in GaN-based superlattice structures grown by plasma-assisted molecular beam epitaxy (MBE) is presented. Careful control of the growth parameters resulted in reduced threading dislocation density as well as optimized interfaces for the superlattices. Intersubband absorption has been observed from a variety of configurations involving GaN single or asymmetric double quantum wells with either thick Al x Ga 1-x N barriers or short-period GaN/Al x Ga 1-x N superlattice barriers. The peak wavelength of absorption can be varied between 1.4-4.2 μm by changing the quantum well thickness. Electron scattering times were measured by the pump-probe technique and were found to be 240-330 fs at 1.55 μm. In addition, intersubband transitions have also been observed for GaN/AlN superlattices grown with a non-polar (1120) orientation.

Improved-efficiency positive and negative luminescent light-emitting devices for mid-infrared gas-sensing applications

InAs/InAsSb SQW LEDs incorporating AlAs0.02Sb0.98 or In0.83Al0.17As electron confining barrier layers are reported. Devices emitting 108 (mu) W and 84 (mu) W at 300 K with QW emission at (lambda) equals 4.1 micrometer and (lambda) equals 4.7 micrometer exhibit quantum efficiencies that are improved by factors of 7 and 3.4 respectively over control samples without the barrier. The operating wavelength of negative luminescent (NL) devices with InAs/In(As,Sb) strained-layer-superlattice (SLS) active regions has been extended to (lambda) equals 6.8 micrometer. NL performance is limited by leakage currents that originate in the n+ contact layer.

Optical studies of InAs/In(As,Sb) single quantum well (SQW) and strained-layer superlattice (SLS) LEDs for the mid-infrared (MIR) region

We report on electroluminescence and photoluminescence studies of arsenic rich InAs1-xSbx heterostructure LEDs for the MIR region. Single-quantum- well LEDs have demonstrated 300 K of approximately 24 (mu) W and approximately 50 (mu) W and approximately 8 micrometers , respectively, with corresponding internal quantum efficiencies of 0.8% and 1.6%. We also demonstrate 4.2 micrometers , 300 K emission from strained-layer superlattice (SLS) LEDs with AlSb electron confining barriers with output powers > 0.1 mW. In reverse bias, these SLS devices exhibit negative luminescence efficiencies of approximately 14% at 310 K.

Print and perish

Although the Internet has fundamentally changed the way we communicate, science publishing is remarkably hesitant in making full use of the potential offered by new technology.