McGill Group Makes Electrically Injected Rolled-up Semiconductor Laser
a) Schematic of the electrically injected free-standing rolled-up tube laser on InP substrate. (b) Measured current-voltage characteristic of the device at room temperature.
Researchers from McGill University, Canada, have demonstrated electrically injected rolled-up semiconductor tube lasers, which are formed when a coherently strained InGaAs/InGaAsP quantum well structure is selectively released from the underlying InP substrate.
An electrically injected, low threshold micro- or nanoscale laser that can be integrated on a silicon platform would be ideal for future chip-level optical communications, driven by the increasing demand for high data rate and low energy budget.
Various types of optical micro-/nanocavities are being considered but among them rolled-up semiconductor tubes (made by selectively releasing strained nanomembranes from their host substrates) exhibit unique characteristics, including ultra-high Q-factors, directional emission, and controlled polarisation.
Moreover, exact tailoring of the optical emission characteristics can be achieved using standard photolithography processes. A further advantage of rolled-up tube optical cavities is that they can be transferred onto a silicon platform without performance degradation, enabling the seamless integration with waveguides, modulators, and other electronic and photonic components.
Recently, optically-pumped rolled-up tube lasers incorporating self-organised quantum dots, quantum dashes, or quantum wells as the gain media have been demonstrated at both low temperature and room temperature. But to date, an electrically injected rolled-up semiconductor tube laser has not been reported.
The difficulty in achieving electrically injected lasing of rolled-up tubes, or other whispering-gallery-mode (WGM) based cavities, lies in the highly inefficient carrier injection process of a conventional vertical p-i-n structure, due to the very thin nanomembranes. Also, the optical performance, including the WGM profiles and Q-factor, can be adversely affected by the presence of electrical contacts and the heating effect, due to the large resistance and large surface recombination.
Dastjerdi and colleagues at the Department of Electrical and Computer Engineering at McGill, have investigated the design, fabrication, and characterisation of electrically injected InP/InGaAsP rolled-up tube lasers, in which multiple InGaAs quantum wells are incorporated as the gain media. In their paper in Applied Physics Letters, they explain that efficient carrier injection into the device active region can be achieved using a lateral carrier injection scheme without compromising the optical emission characteristics.
The resulting devices exhibit strong coherent emission in the wavelength range of 1.5Âµm, with a lasing threshold of 1.05mA for a rolled-up tube with a diameter of 5Âµm and wall thickness of 140nm at 80K. The Purcell factor is estimated to be 4.3.
According to the researchers, such devices can be readily transferred on silicon substrates, providing an electrically injected coherent light source for applications in chip-level optical communications.
'An electrically injected rolled-up semiconductor tube laser' by Dastjerdi et al, Appl. Phys. Lett. 106, 021114 (2015); http://dx.doi.org/10.1063/1.4906238