Design and optimization of GaAs∕AlGaAs heterojunction infrared detectors

Abstract

Design, modeling, and optimization principles for GaAs/ AlGaAs heterojunction interfacial workfunction internal photoemission (HEIWIP) infrared detectors for a broad spectral region are presented. Both n-type and p-type detectors with a single emitter or multiemitters, grown on doped and undoped substrates are considered. It is shown that the absorption, and therefore responsivity, can be increased by optimizing the device design. Both the position and the strength of the responsivity peaks can be tailored by varying device parameters such as doping and the thickness. By utilizing a resonant cavity architecture, the effect of a buffer layer on the response is discussed. Model results, which are in good agreement with the experimental results, predict an optimized design for a detector with a peak response of 9 A / W at 26 m with a zero response threshold wavelength 0 = 100 m. For a 0 =15 m HEIWIP detector, background limited performance temperature (BLIP temperature), for 180°field of view (FOV) is expected around 80 K. For a 0 =70 m optimized design, a highly doped n-type substrate could increase the peak detectivity from 1.7ϫ 10 10 to 3.4ϫ 10 10 Jones at a FOV= 180°operated at temperatures below T Ͻ T BLIP =13 K. Intrinsic response times on the order of picoseconds are expected for these detectors.

Analysis of Barrier Parameters on the Extended Threshold Wavelength of Infrared Detectors

“…The heterostructure detectors operate based on the internal photoemission process (IPE) process where carriers are photoexcited and escape from one material to another by passing through an absorber/barrier interface [9,12]. The photoemission efficiency is proportional to ( )   -, where is the energy of the photo-excited holes and is the potential energy barrier at the interface.…”

“…In general, by increasing thickness of p-GaAs absorber, the absorption in material increases which can change the position of the peak responsivity and spectral width of photoresponse up to a certain limit [9,11]. Since, the Al x Ga 1-x As barriers are undoped and will not produce any photo carriers; therefore the thickness differences don"t have any contribution in the extension of threshold wavelength beyond t .…”

“…The carrier transport over takes place via thermionic emission (since the barriers are thick enough, tunneling can be ignored) [9]. The dark current of a heterostructure detector is described by a 3D carrier drift model [9,10], and for a given value of the electric field, the   kT T I dark    exp 2 3 and ∆ = 1.24/ t . Therefore the dark current of all the detectors is determined by the designed value of and remains unaffected.…”

Quantum structures for multiband photon detection

“…The offset between the Fermi level in the emitter layer and the valence band edge of the barrier layer gives the interfacial workfunction Ä. For HIWIPs, Ä arises due to the band gap narrowing of a highly doped emitter layer [21], while for HEIWIP, the band offset of different materials [22] also contributes to Ä. The threshold wavelength ë c (in µm) is calculated by 1240/Ä, where Ä is in meV.…”

“…Both HIWIP and HEIWIP detectors [21,22] were studied as FIR detectors. Here, the focus will be on dual band detection.…”