V. Trinité

Quantum well infrared photodetectors: present and future

A review of the III-V Lab activities in the field of quantum well infrared photodetectors (QWIPs) is presented. We discuss the specific advantages of this type of detector and present the production facilities and status. A large section is dedicated to broadband QWIPs for space applications and to QWIPs on InP for mid-wavelength infrared detection. We review the progress of QWIP technology for the next generation (dual band, polarimetric, and multispectral) of thermal imagers. Finally, the state-of-the-art of very long wavelength QWIPs is discussed.

Johnson and shot noises in intersubband detectors

Johnson and shot noises are usually considered as independent in intersubband detectors. In this paper, we discuss some simple ideas showing that they are actually the equilibrium and far from equilibrium limits of a single phenomenon. We present an intuitive framework to consistently understand and model these noises in unipolar detectors, in order to enlarge the toolbox of quantum designers.

Monolithic tunable single source in the mid-IR for spectroscopy

We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm-1 with 60 cm-1 tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5μm.

Predictive circuit model for noise in quantum cascade detectors

Electronic noise in quantum cascade structures is investigated theoretically and experimentally under dark conditions. A model based on a unified and insightful vision of noise generating mechanisms is proposed and describes both thermal and shot noise behaviors. Dark measurements of quantum cascade detectors operating at 8 μm and 15 μm are retrieved with good quantitative agreement. This model is expected to be applicable to other quantum structures and under illumination.

Long range resonant tunneling in quantum cascade structures

Tunneling transport in a quantum cascade detector is investigated. With regard to coherent transport in quantum cascade lasers, a Kazarinov–Suris approach R. F. Kazarinov and R. A. Suris, [Sov. Phys. Semicond. 6, 120 (1972)] needs to be modified through the introduction of an additional Fermi–Dirac factor in order to properly model the experimental data at low temperature. Electronic current is completely dominated by tunneling transport; the model here presented should help to suppress it in the future design of efficient quantum cascade detectors.

Comparative study of SiO 2 , Si 3 N 4 and TiO 2 thin films as passivation layers for quantum cascade lasers

The aim of this article is to determine the best dielectric between SiO2, Si3N4 and TiO2 for quantum cascade laser (QCL) passivation layers depending on the operation wavelength. It relies on both Mueller ellipsometry measurement to accurately determine the optical constants (the refractive index n and the extinction coefficient k) of the three dielectrics, and optical simulations to determine the mode overlap with the dielectric and furthermore the modal losses in the passivation layer. The impact of dielectric thermal conductivities are taken into account and shown to be not critical on the laser performances.

Reduction of noise in very long wave infrared quantum cascade detectors

Noise in quantum cascade detectors is studied experimentally and theoretically. Measurements were performed in dark conditions on a quantum cascade detector operating at 14.5 μm, in the very long wave infrared range. To investigate the signal-to-noise contributions of each intersubband transition involved in the transport, a model of noise has been developed. It is based on a noise equivalent electrical circuit of the quantum cascade detector. Non-radiative diagonal transitions (fundamental state to levels of the cascade structure) are identified as dominant contributions to the dark current and noise in the measured device. Based on these theoretical considerations, new optimized structures for the very long wave-infrared range are designed and exhibit a noise reduction down to a factor three at optimum responsivity.

Flexibility properties of type-II InAs/GaSb SL to design MWIR pin photodiodes

InAs/GaSb superlattice (SL) is a peculiar quantum system for infrared detection, where electrical and optical properties are directly governed by the composition and the periodicity of the InAs/GaSb cell. Indeed, several structures with different InAs to GaSb thickness ratios in each SL period, can target the same cut-off wavelength. Likewise, the type of conductivity of the non-intentionally doped SL structure is also linked to the InAs/GaSb SL period. The objective of this communication is to use the flexibility properties of InAs/GaSb SL to design and then to fabricate by MBE a pin photodiode where the active zone is made of different SL periods. Electrical and electro-optical characterizations are reported. The results show that SL structure for the MWIR domain can be designed by combining the best of each SL periods.

Broadband quantum cascade lasers monolithically multiplexed on Silicon for mid-infrared spectroscopy

We present the realizations of an array of Distributed Feedback (DFB) lasers and passive optical waveguides based on Silicon. The aim of these preliminary results is to realize a monolithic, widely tuneable, source in the mid-Infrared (mIR) for laser spectroscopy.

Analysis of electrical and electro-optical characteristics of midwave infrared InAs/GaSb SL pin photodiodes

In this communication, we examine the influence of the SL period of InAs/GaSb superlattice (SL), with diverse InAs to GaSb thickness ratio, on the material and device properties of midwave infrared pin photodiodes. Three SL devices made of three different periods, but exhibiting the same cut-off wavelength at 5 μm at 77K, were grown by molecular beam epitaxy on p-type GaSb substrates. Optical and electrical characterizations (photoluminescence, current-voltage, capacitance-voltage, and photoresponse measurements) were performed and analyzed in order to explain the results obtained. Our investigations show the strong influence of the SL composition on both the material and photodetector properties, such as residual doping concentration, shape of the response spectra and dark current values.