Near and far infrared photon detection techniques in semiconductors

Abstract:

 This study presents three different infrared photon detection techniques based on (a) dye-sensitized photoexcitation in nanostructured semiconductor films (b) spin split-off transition in GaAs/AlGaAs heterostructures, (c) free carrier absorption in GaSb homojunctions. 

In the process known as dye-sensitization, dye molecules bonded to a semiconductor surface inject carriers to a band on photoexcitation. A near-infrared (NIR) sensitive heterojunction n-TiO₂ /Dye/ p-CuSCN was    developed to examine the possibility of adopting dye-sensitization for IR detection at room temperature. Although the detectivity is lower and the response slow compared to silicon detectors, dye-sensitized detectors would be cost effective, especially for large area devices. They are operable at room temperature and have the advantage of insensitivity to noise induced by band-gap excitations (providing high specific detectivity (D*) of, ~10¹¹). Furthermore, the spectral response can be adjusted by choosing the appropriate dye.

Heterojunction interfacial work function internal photoemission (HEIWIP) detectors were used to demonstrate infrared response originating from hole transitions between light/heavy hole bands and the split-off (spin-orbit) band. A GaAs/AlGaAs heterojunction with a threshold wavelength of ~20 μm indicated an operating temperature of 130 K for split-off response in the range of 1.5–5 μm with a peak D* of 1.0×10⁸ Jones. Analysis suggests that devices with optimized parameters are capable of achieving room temperature operation with higher specific detectivity. Feasible approaches to tailor the threshold of the split-off response to different wavelength ranges using different materials such as phosphides and nitrides are also discussed.

A GaSb based homojunction interfacial workfunction internal photoemission (HIWIP) detectors were developed to demonstrate far-infrared (>30μm, known as Terahertz range) response originating from free carrier absorption (hole transitions between light heavy hole bands). Metal-organic vapor phase epitaxy grown p-GaSb/GaSb samples show 9.7 A/W peak responsivity and a peak detectivity of 5.7×10¹¹ Jones with effective quantum efficiency of 33% at 36 μm and 4.9 K. The detector exhibits 97 µm (~3 THz) free carrier response threshold wavelength. Using HEIWIP structures like GaSb/In_xGa_1-xSb would give a flexible system to control the threshold. Estimate indicates that 1 THz (300 μm) threshold could be achieved by varying In fraction. Hence GaSb/In_xGa_1-xSb HEIWIP detectors are promising and could be a potential competitor for THz applications.