Optical: Nanoengineering of InAs Quantum Dot Medium for High Speed Vertical Cavity Lasers

Suny At Albany, Albany NY

Investigators

Abstract

0334994 Oktyabrsky High-frequency directly modulated Vertical Cavity Surface Emitting Lasers (VCSELs) and dense VCSEL arrays are expected to change the whole paradigm of short-range interconnections. Substitution of electrons with photons is expected to dramatically increase bandwidth and reduce power of interconnects ranging from silicon IC I/O's to module- and board-level. Quantum Dots (QDs) due to their discrete electronic spectrum have fundamental advantages over quantum wells that could benefit performance characteristics of laser diodes. The proposal addresses nanoengineering of both homogeneous and inhomogeneous electronic spectra of quantum dots to achieve the performance of the gain medium suitable for utilization in high-speed VCSELs for short range (down to off-chip I/O) optical interconnects. The major target performance characteristics of the device include direct modulation bandwidth >40 GHz, low-power operation of a few mW, and operation temperatures up to 100 0C, necessary for direct integration with a Si chip. The approach involves: (i) development of MBE-related nanoengineering methods to control size, density, shape, and ultimately electronic spectrum and transient phenomena in self-assembled InAs multilayer QDs; to provide minimum size dispersion of the QDs; give the means for shape engineering to increase wave function overlap integral and accelerate the relaxation dynamics to the lasing state; reduce evaporation of carriers from the dots. (ii) Band-structure engineering and implementation of high speed VCSEL structure for QD medium to increase microcavity Q-factor; reduce relaxation time onto the QD ground (lasing) states via application of resonant tunnel junction for direct injection into the QD ground state; reduce series resistance and parasitic capacitance. The work plan includes theoretical analysis and simulation of the QD laser heterostructures; development of QD active medium with high gain and fast capture and relaxation times using control of growth kinetics, band-structure and shape engineering, and doping; testing of the gain medium in edge-emitting laser diodes; design and implementation of VCSELs with tunnel injection heterojunctions; systematic characterization and testing of the QD structures and test devices using in-situ RHEED, and ex-situ SEM, SPM, FIB-cross sectioning, analytical TEM, photoluminescence, electrical DC and microwave methods.