InP Quantum Dot Lasers

The aim is to develop short wavelength quantum dot lasers (640-780nm) for operation at the technologically important wavelengths in the red part of the spectrum.

This makes use of InP quantum dots grown on AlGaInP and ultimately on GaAs substrates. A complementary aim is to gain further insight into the physics of low-dimensional solids as applied to semiconductor lasers.

Interest is driven by the potential for low threshold current density (Jth), reduced temperature sensitivity of Jth and reduced sensitivity to processing induced damage while operating in a wavelength range appropriate for sensing, medical and biophotonic applications.

Activities

Some of our specific achievements to date include:

The development of low threshold current density (150Acm-2 at 300K for 2mm long lasers with uncoated facets), which is only a factor of 2 poorer than the best, longer established, InAs lasers with the same optical loss, and over a wide wavelength range.
Use of Ga composition of dot capping layer alone to adjust the emission wavelength of the quantum dot states (696-750nm).
Understanding of the physics of the temperature dependence of threshold current in these structures, followed by demonstration of significant improvement in the temperature dependence and operation up to 400K.
Measured absorber / gain dynamics prove that the gain exhibits an ultrafast recovery within 200 fs, which is even faster than state-of-the-art InAs/GaAs quantum-dot amplifiers and is promising for optical signal processing at high bit rates.
Measured alpha factor similar to InGaAs dots.

Findings

Further advances are required in:

Understanding and developing temperature insensitive operating wavelength.
Development of DBR lasers producing multi-wavelength output from the same gain medium.
Development of monolithically integrated lasers, detectors and fluid channel for lab-on-a-chip application.