Terahertz photonics

Abstract:

Broadband photoconductive terahertz detectors based on undoped InP single nanowires were demonstrated. By further design and growth of an axial n+-i-n+ structure to reduce the contact resistance, highly-sensitive n+-i-n+ InP single-nanowire terahertz detectors were achieved.

Abstract:

Precise control over the electrical conductivity of semiconductor nanowires is a crucial prerequisite for implementation into novel electronic and optoelectronic devices. Advances in our understanding of doping mechanisms in nanowires and their influence on electron mobility and radiative efficiency are urgently required. Here, we investigate the electronic properties of n-type modulation doped GaAs/AlGaAs nanowires via optical pump terahertz (THz) probe spectroscopy and photoluminescence spectroscopy over the temperature range 5K-300K. We directly determine an ionisation energy of 6.7±0.5meV (T = 52K) for the Si donors that create the modulation doping in the AlGaAs shell. We further elucidate the temperature dependence of the electron mobility, photoconductivity lifetime and radiative efficiency, and determine the charge-carrier scattering mechanisms that limit electron mobility. We show that below the donor ionization temperature, charge scattering is limited by interactions with interfaces, leading to an excellent electron mobility of 4360±380cm2V-1s-1 at 5 K. Above the ionization temperature, polar scattering via longitudinal optical (LO) phonons dominates, leading to a room temperature mobility of 2220±130cm2V-1s-1. In addition, we show that the Si donors effectively passivate interfacial trap states in the nanowires, leading to prolonged photoconductivity lifetimes with increasing temperature, accompanied by an enhanced radiative efficiency that exceeds 10% at room temperature.

Abstract:

How much internet traffic did you generate today? Perhaps more than you realise given the increasing popularity of streaming audio or video content, “cloud” data storage, and social media. It is estimated that approximately 1 zettabyte (1021 bytes) of internet traffic was transmitted globally last year,1 which is the equivalent of about 360MB per day per person in the world. Much of the long distance, high volume internet traffic is transmitted via near infrared (NIR) light through optical fibre waveguides. At the end of the optical fibre the optical signal is turned into an electrical signal, typically for use in silicon based integrated circuits. However, presently most receivers for long distance optical fibre communications systems are based on photodiodes made from other semiconductors such as InxGa1-xAs, or Ge which are challenging and costly to integrate with silicon CMOS electronics on a single chip.