PhD thesis supervisor: dr. Jonas Gradauskas (apply for recommendation)
Investigation of ratchet-based semiconductor sensor of pulsed laser radiation
Modern employment of lasers, both in science and industry, raises requirements for sensing of their radiation. As for infrared detectors, they are classified into two types, thermal and quantum. Thermal detectors (thermocouple, bolometer, pneumatic cell, pyroelectic detectors) use the infrared energy as heat. Therefore, their sensitivity does not depend on radiation wavelength. They do not require cooling, but suffer from slow response time and low detection capability. Quantum, detectors (photoconductive or photovoltaic) demonstrate higher detection properties including faster response speed, but their sensitivity is wavelength-dependent since it is bound up with a semiconductor bandgap and, as a rule, their performance requires cryogenic cooling.
Operation of the sensor is based on the hot carrier effect. Radiation heated charge carriers are redistributed within a nanometre thick semiconductor structure featuring a periodic asymmetric electric potential, which results in a photovoltage (or photocurrent) between the sensor terminals. It combines the best properties of the detectors described above: high response speed, no need for cooling, and a broad, uniform spectral operating range covering both the infrared and visible regions. Its fabrication is not complex: MBE growth together with conventional semiconductor processing. This sensor can also serve as the basis for developing a 2D laser radiation imaging array.