Lydie Dua

Dielectric microcavity in GaN/Si

We have demonstrated an original approach for fabricating microcavities in GaN grown on Si. Holes are etched in the Si substrate and highly reflective dielectric mirrors are deposited on both front and back sides. The cavity has been optically characterized and the results validate our approach.

Two color QWIP and extended wavebands

Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs and related III-V compounds, at THALES Research and Technology Laboratory. The QWIP technology allows the realization of large staring arrays for Thermal Imagers (TI) working in the long-wave infrared (LWIR) band (8-12 μm). In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key parameter for the production to start. The 640x512 LWIR focal plane arrays (FPAs) with 20μm pitch was the demonstration that state of the art performances can be achieved even with small pixels. This opened the field for the realization of usable and affordable megapixel FPAs. Thales Research & Technology (TRT) has been developing third generation GaAs LWIR QWIP arrays for volume manufacture of high performance low cost thermal imaging cameras. In the past, another widely claimed advantage for QWIPs was the so-called band-gap engineering and versatility of the III-V processing allowing the custom design of quantum structures to fulfil the requirements of specific applications such as very long wavelength (VLWIR) or multispectral detection. In this presentation, we present the performances of both our first 384x288, 25 μm pitch, MWIR (3-5μm) / LWIR (8-9 μm) dual-band FPAs, and the current status of QWIPs for MWIR (< 5μm) and VLWIR (>15μm) arrays.

A high performance quantum-well infrared photodetector detecting below 4.1 µm

We demonstrate a high performance quantum-well infrared photodetector on GaAs(0 0 1) substrate, with a spectral response peaked below the carbon dioxide absorption band. The active layer is based on an AlGaAs/AlAs/InGaAs/AlAs/AlGaAs quantum well and designed to achieve a bound to quasi-bound transition. The external quantum efficiency measured at 130 K and –1 V is as high as 21%, leading to peak absorption higher than 28% when an anti-reflection coating is used. The background limited peak detectivity reaches 7 × 1011 Jones (cm Hz1/2 W−1) at 77 K and f/1.6. The detector operates in the background limited regime up to 100 K. Our measured characteristics are key inputs to estimate the performance of a thermal imager and are directly useable by system designers.

QWIP from 4μm up to 18μm

Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIP) are considered as a technological choice for 3rdgeneration thermal imagers [1], [2]. Since 2001, the THALES Group has been manufacturing sensitive arrays using AsGa based QWIP technology at THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays for Thermal Imagers (TI) working in the Infrared region of the spectrum. The main advantage of this GaAs detector technology is that it is also used for other commercial devices. The GaAs industry has lead to important improvements over the last ten years and it reaches now an undeniable level of maturity. As a result the key parameters to reach high production yield: large substrate and good uniformity characteristics, have already been achieved. Considering defective pixels, the main usual features are a high operability (> 99.9%) and a low number of clusters having a maximum of 4 dead pixels. Another advantage of this III-V technology is the versatility of the design and processing phases. It allows customizing both the quantum structure and the pixel architecture in order to fulfill the requirements of any specific applications. The spectral response of QWIPs is intrinsically resonant but the quantum structure can be designed for a given detection wavelength window ranging from MWIR, LWIR to VLWIR.

Focal Plane Arrays from UV up to VLWIR

Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on GaAs and related III-V compounds, at the Alcatel-Thales-III-V Lab (formerly part of THALES Research and Technology Laboratory). In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and has been the key parameter for the production to start. Another widely claimed advantage for QWIPs was the so-called band-gap engineering and versatility of the III-V processing allowing the custom design of quantum structures to fulfil the requirements of specific applications such as very long wavelength (VLWIR) or multispectral detection. In this presentation, we give the status of our LWIR QWIP production line, and also the current status of QWIPs for MWIR (<5μm) and VLWIR (>15μm) arrays. As the QWIP technology cannot cover the full electromagnetic spectrum, we develop other semiconductor compounds for SWIR and UV applications. We present here the status of our first FPA realization in UV with GaN alloy, and at 1.5μm with InGaAs photodiodes.

Design of broadband QWIPs

One of the key features of quantum well infrared photodetectors is the narrow absorption band. However, some applications, as the infrared spectroscopy, require broadband detection. Several approaches have been used to get a broadband response with QWIPs (superlattices, digital graded barriers, stacks, etc.). In this paper, we focus on the interlaced configuration and on the coupled wells structure. Both designs exhibit broadband response covering the [11-15 μm] spectral range. The experimental dependencies of the spectral shape versus the temperature and bias voltage are discussed. Based on numerical model, we propose a specific design strategy which leads to a spectral shape quasiindependent on the operating conditions.