The objective of this research is to design, epitaxially grow, fabricate, characterize, and analyze optically pumped and electrically injected subwavelength nanoscale rolled-up In(Ga)As quantum dot 1.3µm lasers that can demonstrate ultra low threshold (< 100µA) at room temperature. The inherent advantage offered by quantum dot tunnel injection heterostructure for nanoscale laser operation, such as large gain, low threshold and high quantum efficiency will also be investigated. The transformative impact of this research is the availability of a low power and compact laser for interconnects and for spectroscopy.
Intellectual Merit The intellectual merit is the first demonstration of nanoscale rolled-up subwavelength sized laser on GaAs, that can be optically or electrically pumped. Demonstration of a reliable room temperature nanoscale laser on GaAs/InP is also transformative and is considered as a milestone in optoelectronics. The rolled-up technique and associated device fabrication are more simple than other techniques for nanoscale lasers that are currently being explored.
Broader Impacts The broader impacts of the proposed research include social, economic and educational benefits. Ultra-low power light sources reduce energy consumption and help in transmitting information efficiency and at faster rates. The interdisciplinary nature of the program will provide an excellent training ground for graduate and undergraduate students - our future work force in several critical areas. Training of women and underrepresented minorities in summer programs in the general areas of optoelectronics and lighting will be a priority. K-12 outreach will include demonstrations during visits and creating a broader awareness for science and mathematics.
Rolled-up microtube is a novel microcavity that is formed by releasing ultrathin strained epilayer from the host substrate. Insertion of a gain medium such as quantum dots or quantum wells inside the rolled-up microtube makes it an interesting laser cavity since the microtube walls are atomistically smooth and it has a near perfect overlap between the optical field and the gain medium which in turns reduces the threshold of operation. Another interesting property of the rolled-up microtube devices (microtube lasers, microtube detectors etc.) is that they can transferred on to silicon substrate and therefore they could one day find applications in future on-chip optical communication. Moreover, the unique hollow geometry of the microtubes makes them interesting for fluid sensing applications. A novel InAs/GaAs quantum dot rolled-up microtube laser formed by an epitaxial strain-driven mechanism has been investigated. Simplified analytical expressions have been derived for the scattering (radiation) loss at the microtube notches, the bending loss, and the substrate loss and their values have been calculated as a function of tube diameter. The threshold condition for a microtube laser has been derived from which it is found that the threshold excitation (power) is inversely proportional to the microtube diameter which has been verified with experimental data. A rolled-up microtube active directional coupler made of twin microtubes is demonstrated. The microtube is made of an InGaAs/GaAs strained bilayer with InAs self-organized quantum dots inserted in the GaAs layer. The directional coupler can work in both active and passive modes and therefore can be excited with light of any wavelength. The coupling characteristics have also been measured in isopropyl alcohol, instead of air, as the surrounding media to demonstrate the potential of the device as a sensor. A quantum dot rolled-up microtube optoelectronic integrated circuit operating as a phototransceiver has been demonstrated. The phototransceiver consists of an optically pumped microtube laser and a microtube photoconductive detector connected by a a-Si/SiO2 waveguide. The rolled-up microtube detector exhibits a very low dark current of 9 µA for a bias of 5V and the responsivity of the phototransceiver circuit is 34 mA/W.
