Low threshold current vertical-cavity surface-emitting lasers with enhanced resistance to heating

Abstract

Vertical-cavity surface-emitting lasers (VCSEL's) fabricated by selective oxidation are attractive to achieve ultralow threshold currents [1-3]. Efficient heat dissipation, along with low threshold, is critical for uses as optical interconnects where massive integration is required. In this paper, we report an ultralow threshold of 8.7 µA and a high output power over 1.9 mW in single quantum well VCSEL's fabricated by selective oxidation from an all epitaxial structure with intracavity p-contact layers grown by metalorganic chemical vapor deposition. The design of this structure is optimized for low thermal resistance by using distributed Bragg reflectors (DBR's) composed completely of binary materials. Fig.l shows a schematic cross-section of the fabricated VCSEL's. The epitaxial structure consists of a 30-pair n-doped AlAs/GaAs quarter-wave stacks, an Al0.22Ga0.78As/GaAs/In0.2Ga0.8As resonant λ-cavity, p-doped contact layers, and a 22-pair undoped AlAs/GaAs quarter-wave stacks. The p-doped contact layers are formed from a 0.25 λ AlAs current constriction layer and a 0.75 λ GaAs intracavity contact layer. After growth, the top DBR is selectively wet etched into 14 and 5 µm square mesas down to the p-type GaAs contact layer. Then, 50 µm square mesas, whose centers coincide with the centers of the top mesas, are formed by wet chemical etching. Current flow apertures of 10 and ~3 µm are formed below the 14 and 5 µm square top mirrors, respectively, by selective oxidation.