Bandgap Theory and Quantum dots LASER

I have worked on quantum dots lasers grown by Phillip Poole and Pedro of Canada Research Council (NRC) in Ottawa to determine their operating characteristics using temperature and high hydrostatic pressure.

Temperature measurements help us to determine how the device inner workings cope with temperature. by the way my PhD research is aimed at finding ways to make semiconductor LASER devices temperature insensitive. Most of LASER devices in the market suffer from temperature dependence and hence require very expensive cooling systems. Meaning as temperature increase the performance of the devices decrease dramatically.

This effect can be seen by an increase in threshold current due to increase in Non-radiative recombinations of the carriers in the active medium. Ideally we should have only radiative recombinations which will be a result of injected photons exciting electrons to higher level and these excited electrons to release a photon on their way down to lower energy levels and hence perfect laser.

Sadly at room temperature the dominant process is non-radiative recombination named Auger recombination process which is thermally activated. this process is a major source of loss as the photon from de-excited electron is given to a third carrier which is turn excited further into higher level or vacuum. at room temperature radiative recombination could account to approx 6 percent of all threshold current. the rest is to just counter the effect of Auger at room temperature in devices i worked on.

Pressure measurement involves squeezing the device in high pressure about 10kbar, this is equivalent of standing five grown African Elephants on a 1 cm square area. this allows one to change the interatomic spacing between the atoms in the crystal lattice. In doing so the band gap changes as you increase pressure the band gap is increased in most four-five semiconductor devices.

more information can be found in my paper published by American Physics Letters (APL) in October 2010 title of the paper is Efficiency Limiting Processes in 1.55 micron InAs/InP-Based Quantum Dots Lasers.