A new approach to quantum well infrared photodetectors: Staircase-like quantum well and barriers
Introduction
After the first quantum well infrared photodetector (QWIP) based on inter-subband absorption between two bound quantum well states was demonstrated by Levine et al. [1], there have been great progress made in QWIPs for infrared detection. Based on mature III–V materials technology such as GaAs/AlGaAs structures, QWIPs have potential advantages promising high sensitivity, low power, low cost, high performance focal plane arrays and monolithic integration with high speed electronic devices [2]. All these advantages make them desirable in applications such as advanced sensing and imaging systems. A large number of QWIP structures have, to date, been investigated. These include large inter-subband absorption due to bound-to-bound transition [1], inter-subband absorption due to bound-to-continuum transition [3], voltage tunable multicolor QWIPs [4], broad-band QWIPs [5].
In this paper, we present a theoretical study of a novel staircase infrared detector, which was studied as a light emitter by us [6], based on the GaAs/AlGaAs material system with varying Al concentrations in the quantum wells and barriers. The detection wavelength is around 12 μm, at room temperature. The optical transitions investigated are inter-subband bound-to-bound transitions. Since at zero bias, the device contains staircase-like quantum wells and barriers, dark current is dramatically lower compared to other QWIPs in the literature [7], [8], [9].
Section snippets
Device structure
The device structure, which we investigate, is an n+–i–n+ three-well system, consisting of Ga1−xAlxAs quantum wells and barriers where concentration, x, varies from 0 to 0.43. The exact composition and the thickness of all quantum wells and barriers as well as the doping concentrations are given in Table 1. The resulting device parameters including the potentials and bound state energies are given in Table 2. Here, () shows the distance of the left hand side of the nth barrier (well)
Theoretical considerations
Potential energy of the system shown in Fig. 1 can be given aswherewhere S is the step function andHamiltonian of the system can be written asSince the band bending of the structure can be omitted at steady state, eigenfunctions of the Hamiltonian in the wells and barriers are of the following form:Here, the , wave numbers of wells and barriers, for the
Results and discussion
The calculated energy levels of the quantum wells and relevant parameters are given in Table 2. The potential energy profile of the structure and squared wave functions are shown in Fig. 1. The energy level differences between and , and are approximately 15 meV, at zero applied bias. The conduction band potential energy profile of the structure at k = 0 has also been calculated self-consistently by solving Poisson and Schrödinger equations, where effective mass approximation
Conclusions
A new version of the classical quantum cascade structure is proposed to be used as a photodetector operating in the long wavelength infrared range in the GaAs/AlGaAs materials system. The proposed structure makes use of quantum wells and barriers with increasing Al content both in the wells and in the barriers forming a staircase-like energy band diagram without applied bias. This results in very low dark current density, a major problem for most infrared detectors. Growth of the detector
Acknowledgements
We would like to thank The State Planning Organization of Turkey (DPT) for funding this project (Project No: 200190K.120330). S.U.E author thanks Bilkent University Physics Department for their hospitality.
References (13)
- et al.
A two-stack, multi-color quantum well infrared photodetector for mid- and long-wavelength infrared detection
Infrared Phys. Technol.
(2003) - et al.
Intersubband electron transition across a staircase potential containing quantum wells: light emission
Superlattices Microstruct.
(2005) - et al.
Optoelectronic transport mechanism from subband infrared absorption and tunneling regeneration
Current Appl. Phys.
(2002) - et al.
Normal incidence InAs/InGaAs dots-in-well detectors with current blocking AlGaAs layer
J. Cryst. Growth
(2003) - et al.
Modulation-doping in 3–5 μm GaAs/AlAs/AlGaAs double barrier quantum well infrared photodetectors: an alternative to achieve high photovoltaic performance and high temperature detection
Infrared Phys. Technol.
(2003) - et al.
New 10 μm infrared detector using intersubband absorption in resonant tunneling GaAlAs superlattices
Appl. Phys. Lett.
(1987)