GeSn/Ge Multiquantum-Well Vertical-Cavity Surface-Emitting p-i-n Structures and Diode Emitters on a 200 mm Ge-on-Insulator Platform

Abstract

An efficient monolithically integrated light source with complementary metal-oxide-semiconductor (CMOS) compatibility remains the missing component to enable Si photonics for various applications. In particular, vertical-cavity-surface emitting (VCSE) light sources, such as resonant cavity light-emitting diodes (RCLEDs) and vertical-cavity surface-emitting lasers (VCSELs), are strong contenders due to their compact size, circular emission profile with low beam divergence, wafer-scale fabrication compatibility, high bandwidth, and high coupling efficiency to fiber optic cables. We report the first demonstration of 8 in. wafer-scale GeSn/Ge multiple-quantum-well VCSE p-i-n structures and diodes for laser or light-emitting diode (LED) applications in Si photonics by wafer bonding and layer transfer techniques, which are challenging for all-epitaxy routes. The wafer could be 12 in. (300 mm) since the MQW gain medium is grown on a 300 mm Si wafer, and the bonding is wafer-scale. Alternative dielectric layers (SiO2/SiN/SiO2), introduced by wafer bonding, under the emitting structure, serve as the bottom mirror for the vertical cavity. The Ge0.92Sn0.08/Ge MQW layer is utilized to improve the material quality and to confine injected carriers. As a result, more than 8x enhancement of light emission due to the vertical cavity resonance was demonstrated by photoluminescence spectroscopy. Besides, the spectral purity is enhanced by the single-longitudinal-mode cavity. The intensity of light emission is insensitive to the temperature range from 4 to 300 K and even becomes stronger at higher temperatures since the stronger resonant cavity effect at higher temperatures compensates for the drop in light emission efficiency caused by nonradiative centers. The vertical cavity effect on the light emission is further verified by reflectivity spectroscopy and optical simulations. A positive gain can be achieved as indicated by optical gain calculations. Room-temperature electroluminescence and an excellent carrier injection efficiency of the MQW VCSE diode are observed, showing its potential for electrically injected RCLEDs and VCSELs.