At room temperature, we demonstrate an unambiguous detection of the ground- and excited-state transitions of mid-infrared GaInSb/AlGaInSb type I quantum well (QW) lasers grown on GaAs using a new technique based on Fourier transform infrared surface photovoltage spectroscopy. It is found that none of the currently established spectroscopic techniques is able to detect even the ground state transition of these mid-infrared QW lasers at room temperature. The spectroscopic results are in reasonable agreement with the laser emission spectra at low temperatures.

A novel application of the surface photovoltage spectroscopy (SPS) technique, using a Fourier transform infrared (FTIR) interferometer, has been developed for the investigation of narrow‐gap mid‐infrared semiconductor quantum well (QW) laser structures. We demonstrate the FTIR‐SPS technique at room temperature for a GaInSb/AlGaInSb type I QW laser structure, grown on GaAs, emitting in the mid‐infrared at ∼4 μm, revealing an unambiguous detection of the ground and excited state transitions of the GaInSb QW, as well as the AlGaInSb barrier bandgap energy. As a further corroboration of the new technique, the FTIR‐SPS spectrum of a ∼1.5 μm communication laser structure has also been measured and shown to be in good agreement with conventional grating‐based electro‐modulated reflectance and SPS spectroscopic measurements on this sample. A detailed numerical analysis of the room temperature FTIR‐SPS results for the mid‐infrared semiconductor laser structure is also presented, including a comparison with theoretical predictions of the QW transition energies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, two tri‐metal quaternary InGaAlAs quantum well (QW) laser structures grown on InP are compared to a conventional InGaAsP QW structure, also grown on InP, all designed to lase at 1.55 μm. Several spectroscopic methods are used to study the samples including surface photo‐voltage (SPV) and electro‐modulated reflectance (ER). In the tri‐metal samples the ground‐ and two excited‐state QW transitions are detectable in both types of spectroscopy. The SPV and ER give results in agreement to within a few meV of each other. By comparing the position of the measured QW transitions with those predicted theoretically, the conduction band offsets of the tri‐metal samples can be determined and compared to that in the InGaAsP sample. It is found that the tri‐metal samples have a much larger conduction band offset of ∼66% compared to the ∼40% in the InGaAsP sample. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report angle dependent and temperature dependent (9 K-300 K) photo-modulated reflectance (PR) studies on vertical-cavity surface-emitting laser (VCSEL) structures, designed for 2.3 lm mid-infrared gas sensing applications. Changing the temperature allows us to tune the energies of the quantum well (QW) transitions relative to the VCSEL cavity mode (CM) energy. These studies show that this VCSEL structure has a QW-CM offset of 21 meV at room temperature. Consequently the QW ground-state transition comes into resonance with the CM at 220 6 2 K. The results from these PR studies are closely compared with those obtained in a separate study of actual operating devices and show how the PR technique may be useful for device optimisation without the necessity of having first to process the wafers into working devices. V C 2014 AIP Publishing LLC.

Three GaInSb/AlGaInSb type I multi-quantum-well (QW) laser structures grown on GaAs, with increasingly strained QWs, aimed at emitting at ∼4 μm, are analysed using our Fourier transform infrared surface photo-voltage spectroscopy technique. The measurements clearly yield a full set of transitions including not only the barrier bandgap, but also the QW ground state transition, from which the device operating wavelengths can be inferred, and up to five excited state QW transitions. The full set of measured transition energies are then compared closely with those predicted by an 8-band k • p model which gives a generally good agreement for the QW transitions, but an indication that the current literature values for the AlGaInSb bandgap seem to be in considerable error for the present alloy compositions.