Capacitive infrared photodetector for room temperature operation

Abstract

We report a self-assembled semiconductor nanowire photodetector that detects infrared light at room temperature by registering a change in capacitance upon illumination. Its light-to-dark capacitance ratio exceeds 2.5 at a signal frequency of 75 kHz and gradually decays to 1 beyond 200 kHz. This detector also exhibits “frequency-selectivity” since it is more responsive to photons with energies close to the nanowire's effective bandgap than to higher energy photons. Such a light-sensitive capacitor, unlike a light-sensitive resistor, can be used in a resonant parallel inductor-capacitor circuit to yield giant light-to-dark contrast ratio even when the light-to-dark capacitance ratio is relatively small.

Nanowire-based frequency-selective capacitive photodetector for resonant detection of infrared radiation at room temperature

“…18 It conductance barely changes-but its capacitance changes measurably upon IR illumination. In other words, the conduction current flowing through the detector is virtually insensitive to light, but the displacement current is not.…”

“…It is very clear how light can change the conductance of a semiconductor by generating electron-hole pairs, but it is not so obvious how light can change the capacitance. The physical mechanism of how light can change capacitance is the following: 18 The electron-hole pairs generated by light absorption in a semiconductor do not change the total amount of charge Ð d 3r qðr; tÞ since for every electron created there is a corresponding hole. However, the generated carriers can always change the instantaneous local charge density qðr; tÞ at an arbitrary locationr in the semiconductor at time t. This will change the local instantaneous electric fieldẼðr; tÞ in accordance with the Poisson equatioñ r ÁẼðr; tÞ ¼ qðr; tÞ=, where is the detector material's permittivity.…”

“…18 The starting material is a 99.9999% pure aluminum foil that is diced into 2 cm  2 cm sized coupons. The latter were electropolished in a solution of perchloric acid, butyl cellosolve, ethanol, and distilled water at 40 V for 15 s (in installments of 5 s to reduce heating effects).…”

Nano-scale NiSi and n-type silicon based Schottky barrier diode as a near infra-red detector for room temperature operation

“…5,6 As a result of tunability of capacitance, a shift in resonant peak frequency (in an LC circuit) is observed and accordingly a change in the power delivered to the load. The detectivity is reported to be 3 Â 10 7 Jones.…”

High density near amorphous InSb nanowire arrays and its photo-electric performance

“…The exciton Bohr radius of InSb is about 65.5 nm [21], and the quantum confinement effect will dominate when the diameter of the InSb nanowire is less than its Bohr radius. These properties make it an ideal material for PE and long-wavelength detectors, field-effect transistors (FETs), quantum devices, etc.. [22][23][24][25][26][27][28][29][30][31][32][33] Most of the reported InSb nanowires were crystallinity [14,20]. But reducing the crystal size may be considered as another way towards disorder, which seems favorable as a detector.…”