Vincent Guériaux

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.

Double barrier strained quantum well infrared photodetectors for the 3–5μm atmospheric window

We present a detailed study of double barrier strained Al0.35Ga0.65As/AlAs/GaAs/In0.2Ga0.8As quantum well infrared photodetectors on GaAs substrate. Measurements were made on four different well widths active layers and on several mesa pixels with different optical coupling structures. We obtained responses peaked in the spectral range 3.6–4.6 μm. Based on the experimental results, we show that in the background limited regime, the impact ionization is the restrictive transport process for midwave detectors. We also demonstrate a 4 μm structure with the high background limited detectivity of 2×1011 Jones at 77 K and 9×1010 Jones at 110 K (2π field of view, 300 K background).

QWIP status and future trends at Thales

Since 2005, Thales is successfully manufacturing QWIPs in high rate production through III-V Lab. All the early claimed advantages of QWIPs are now demonstrated. The versatility of the band-gap engineering allows the custom design of detectors to fulfill specific application requirements in MWIR, LWIR or VLWIR ranges. The maturity of the III-V microelectronics based on GaAs substrates gives uniformity, stability and high production rate. In this presentation we will discuss the specific advantages of this type of detector. An overview of the available performances and production status will be presented including under-development products such as dual band and polarimetric sensors.

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 infrared detector production line results

Since 1997, Sofradir has been working with Thales Research & Technologies (TRT) to develop and produce Quantum Well Infrared Photodetectors (QWIP) as a complementary offer with Mercury Cadmium Telluride (MCT) Long Wave (LW) detectors, to provide large LW staring arrays. Thanks to the low dark current technology developed by TRT, the QWIP detectors can be operated at FPA temperature above 73K, enabling the production of compact Infrared (IR) cameras thanks to the use of compact microcoolers. The TV/2 VEGA-LW detector (25μm pitch 384×288 Integrated Detector Dewar Assembly (IDDCA)) is integrated in the Catherine-XP thermal imager from Thales Optronique SA (TOSA). To date, more than one thousand units have been manufactured. The TV SIRIUS-LW detector (20μm pitch 640×512 IDDCA) is integrated in the Catherine-MP thermal imager from Thales Optronics Ltd. (TOL). To date, several hundreds of units have been manufactured. We will discuss in this paper statistical results of these productions and our latest reliability study results, which highlight the stability of the TRT QWIP technology. Thanks to this mature technology, TRT and Sofradir have been able to increase the QWIP wafer size from 3 inches to 4 inches, without any impact on yields and FPA performances. A dual-band Mid Wave-Long Wave (MW-LW) QWIP detector (25μm pitch 384×288 IDDCA) is currently under development. We will present in this paper its latest results.

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.

Influence of Sawtooth Patterns on the Detection Properties of Quantum Well Infrared Photodetectors

Sawtooth patterns in the I-V curves of superlattices result from the bistability induced by the negative differential resistance of the local J-F curve. This behavior has been extensively studied in weakly coupled superlattices from a transport point of view. In this paper, we show that the sawtooth patterns not only affect the dark current but also the noise and responsivity properties of a quantum well infrared photodetector. Their impact on the imaging properties of the detector is also quantified.