2013-2016 (Fast Track)
2020-2023 (Core Research Grant)
Pump Probe Spectroscopy
Pump probe spectroscopy is a widely used technique to study the dynamics of carriers, phonons and spins in different material systems. In this method, an ultra-short laser pulse which is only about 100-fs long is split into two: a strong beam which is called the pump is used to excite the sample and a weaker beam which is called the probe is used to monitor the pump-induced changes in the properties of the sample as a function of the time delay between the pump and the probe pulses.
TeraHertz Time-Domain Spectroscopy
TeraHertz (THz) region of the electromagnetic spectrum lies between the microwave and the infrared part. By illuminating a biased photoconductive antenna (PCA), THz waves can be generated. THz waves can be detected again using a PCA. Time-Domain Spectroscopy (THz-TDS) is a method to study the far infra-red properties of materials. For THz-TDS, the femtosecond laser pulse is split into to two paths, one path reaches the THz emitter and the other path reaches the THz detector. The time delay between the pulses from the two beams can adjusted using a delay stage. The THz pulse is focussed on the sample and detected after passing through the sample. The THz signal reaching the detector is measured using the detector by employing a lock-in technique. From the measured signal the full complex value of the material parameters can be extracted.
III-V semiconductors doped with small amounts of bismuth (known as dilute bismides) have attracted a lot of interest in the recent years. GaAs:Bi exhibits some unusual properties like giant band gap bowing, and giant spin-orbit bowing. This material has potential technological applications in high-efficiency solar cells, hetero junction bipolar transistors (HBTs), spintronic applications, thermoelectric devices and near-infrared devices. We are addressing some of the fundamental questions related to GaAs:Bi.
GaN:Bi is another interesting dilute Bismide alloy. GaN is a wide band gap (3.4 eV) semiconductor which is commonly used for optoelectronics, high-power and high-frequency applications. For example, GaN HEMTs are used in various wireless infrastructure applications due to their high efficiency and high voltage operation. GaN is suitable for making solar cells for space applications. The addition of Bi will provide a means to tune the band gap of GaN which will be useful for applications such as high-efficiency solar cells, light-emitting diodes, laser diodes and high frequency transistors. The incorporation of Bi in GaN is difficult because of the large differences in atomic radii of N and Bi and there hasn’t been any significant work done on this material. Our collaborators in the UK, has recently shown that it is possible to incorporate Bi in GaN at certain growth conditions. Incorporation of Bi up to 20% in GaN was demonstrated.
We are trying to understand these alloy systems in a better way, which will enable us to exploit these alloys for various device applications in RF, THz, PV and SSL technologies.