P. Christol

Wet etching and chemical polishing of InAs/GaSb superlattice photodiodes

In this paper, we studied wet chemical etching fabrication of the InAs/GaSb superlattice mesa photodiode for the mid-infrared region. The details of the wet chemical etchants used for the device process are presented. The etching solution is based on orthophosphoric acid (H3PO4), citric acid (C6H8O7) and H2O2, followed by chemical polishing with the sodium hypochlorite (NaClO) solution and protection with photoresist polymerized. The photodiode performance is evaluated by current?voltage measurements. The zero-bias resistance area product R0A above 4 ? 105 ? cm2 at 77 K is reported. The device did not show dark current degradation at 77 K after exposition during 3 weeks to the ambient air.

GaSb-based mid-infrared 2–5 μm laser diodes

Laser diodes emitting at room temperature in continuous wave regime (CW) in the mid-infrared (2–5 μm spectral domain) are needed for applications such as high sensitivity gas analysis by tunable diode laser absorption spectroscopy (TDLAS) and environmental monitoring. Such semiconductor devices do not exist today, with the exception of type-I GaInAsSb/AlGaAsSb quantum well laser diodes which show excellent room temperature performance, but only in the 2.0–2.6 μm wavelength range. Beyond 2.6 μm, type-II GaInAsSb/GaSb QW lasers, type-III ‘W’ InAs/GaInSb lasers, and interband quantum cascade lasers employing the InAs/Ga(In)Sb/AlSb system, all based on GaSb substrate, are competitive technologies to reach the goal of room temperature CW operation. These different technologies are discussed in this paper. To cite this article: A. Joullie, P. Christol, C. R. Physique 4 (2003).

Unambiguous determination of carrier concentration and mobility for InAs/GaSb superlattice photodiode optimization

In this communication we report on electrical properties of nonintentionally doped (nid) type II InAs/GaSb superlattice grown by molecular beam epitaxy. We present a simple technological process which, thanks to the suppression of substrate, allows direct Hall measurement on superlattice structures grown on conductive GaSb substrate. Two samples were used to characterize the transport: one grown on a semi-insulating GaAs substrate and another grown on n-GaSb substrate where a etch stop layer was inserted to remove the conductive substrate. Mobilities and carrier concentrations have been measured as a function of temperature (77–300 K), and compared with capacitance-voltage characteristic at 80 K of a photodiode comprising a similar nid superlattice.

Fractional‐dimensional calculation of exciton binding energies in semiconductor quantum wells and quantum‐well wires

We propose a fractional‐dimensional approach of excitonic characteristics in semiconductorquantum wells and quantum‐well wires with cylindrical or rectangular cross sections. This type of approach has proved to provide accurate and convenient methods for extracting excitonic binding energies, either from optical spectroscopy experiments, or from simple envelope function calculations. In this paper, we first try and extend the simple description previously developed for single quantum wells and superlattices. Next, we show how the accuracy of the model is dramatically improved by invoking microscopic considerations, in order to describe the anisotropy of the relative motion of confined electron‐hole pairs. This original approach allows a rather simple and quick determination of eigenenergies of confined excitons, whatever the quantum numbers of the conduction and valence subbands, and whatever the shape of the confining medium. The results of our calculations compare favorably to those of available variational theories and to experimental findings.

Characterization of midwave infrared InAs/GaSb superlattice photodiode

We report on structural, electrical, and optical characterizations of midwave infrared InAs/GaSb superlattice (SL) p-i-n photodiodes. High-quality SL samples, with 1 μm thick active region (220 SL periods), exhibited a cut-off wavelength of 4.9 μm at 80 K. Using a capacitance-voltage measurement technique performed on mesa diode, the residual background concentration in the nonintentionally doped region was determined to be 3×1015 cm−3 at 80 K. Extracted from current-voltage characteristics, R0A products above 4×105 Ω cm2 at 80 K were measured, and the quantitative analysis of the J-V curves showed that the dark current density of SL photodiode is dominated by generation-recombination processes. Front-side illuminated photodiodes produced responsivity at 80 K equal to 360 mA/W at 4.5 μm.

Thermalisation rate study of GaSb-based heterostructures by continuous wave photoluminescence and their potential as hot carrier solar cell absorbers

GaSb-based heterostructures are tested as candidates for a hot carrier solar cell absorber. Their thermalisation properties are investigated using continuous wave photoluminescence. Non-equilibrium carrier populations are detected at high excitation levels. An empirical expression of the power lost by thermalisation is deduced from the incident power dependent carrier temperature. The experimentally determined thermalisation rate is then used to simulate the potential efficiency of a hot carrier solar cell, showing a significant efficiency improvement compared to a fully thermalised single p–n junction of similar bandgap.

A type-II superlattice period with a modified InAs to GaSb thickness ratio for midwavelength infrared photodiode performance improvement

We present a type-II superlattice period with a modified InAs to GaSb thickness ratio for midinfrared detection. In this kind of structure, the large electron-hole wave-function overlap and the low intrinsic carrier concentration lead to a significant signal-to-noise ratio enhancement. For the proof of concept, a sample designed with an InAs to GaSb thickness ratio close to 2 was grown. Comparison with standard design photodiodes shows an improvement of the differential resistance area product by one and a half decade while the quantum efficiency was more than doubled.

Excitons in semiconductor quantum wells: A straightforward analytical calculation

A new and very simple method is presented for calculating exciton binding energies in quantum confined semiconductor structures. The aim of the model calculation, which is developed in the framework of the fractional‐dimensional space, is not to compete with the very advanced ones already proposed but, on the contrary, to avoid tedious and expensive calculations to obtain, with a good accuracy, the exciton binding energy in most of the confined structures. Furthermore, in the cases where the 1s and 2s transition energies can be experimentally measured, the method permits one to obtain the exciton binding energy without any hypothesis nor calculation.

Type-II InAsSb/InAs strained quantum-well laser diodes emitting at 3.5 μm

Mid-infrared laser diodes with compressively strained InAsSb/InAs type-II slightly coupled quantum wells are reported. These lasers, grown on InAs by molecular-beam epitaxy, have emission wavelength near 3.5 μm. They exhibit pulsed operation up to 220 K, with at 90 K threshold current density of 150 A/cm2. Ridge lasers continuous wave (cw) operated up to 130 K with cw output power of 40 mW/A/facet and a characteristic temperature T0=40 K.

Influence of the period thickness and composition on the electro-optical properties of type-II InAs/GaSb midwave infrared superlattice photodetectors

In this paper, the electro-optical properties of InAs/GaSb superlattice (SL) midwave infrared photodiodes with different periods were investigated. Three devices with different SL periods, but the same cut-off wavelength at 5??m at 77?K, were grown by molecular beam epitaxy on p-type GaSb substrates. The optical and electrical behaviours were characterized and analysed. Our investigations show strong influence of the SL composition on both the material properties and photodetector performances, such as the background doping concentration, shape of the response spectra and the dark current behaviours.