Current and heat spreading transparent layers for surface-emitting lasers

Abstract

A surface-emitting laser includes optically transparent layers on a side of a DBR mirror structure that is opposite to an optical cavity of the laser. In one embodiment, the transparent layer is a heat-conducting layer that has an efficient heat transfer relationship with an opening in a top electrode and with a heat-spreading layer. The heat-spreading layer increases the diameter of the electrode, so as to reduce the thermal impedance of the surface-emitting laser. The heat-spreading layer may be annular in shape and may have an inside diameter that is less than the outside diameter of the electrode, allowing the heat-spreading layer to first overlap the electrode and then overlap the portion of the heat-conducting layer that resides on the inside portion of the electrode. In another embodiment, the optically transparent layer is positioned between the top electrode and the top DBR mirror structure of the surface-emitting laser. In this embodiment, the transparent layer is a current-spreading layer that reduces the lateral resistance of the laser. Lateral resistance is reduced by providing a layer having a thickness of one-half of the wavelength of the light energy generated in the laser times an odd multiple greater than one. Optionally, two half-wavelength layers may be formed between the electrode and the mirror structure, with the upper layer being selected primarily for its electrical properties and the lower layer being selected primarily for its optical properties.