Circular Grating Surface-Emitting Laser,

Although surface-normal emission from a laser using a one-dimensional second-order grating has been published for some time, it is only in the last few years that the theory of circular I.E. two dimensional gratings has been considered theoretically. Last year lasing in an optically-pumped circular grating structure was observed . Here we report for the first time lasing at room temperature in an electrically-pumped circular grating laser. The structure of the laser consists of a circular active region with a conventional double heterostructure DH surrounded by a waveguide region. A concentric second-order circular grating patterned on top of it serves the dual purpose of a distributed Bragg reflector DBR for the inplane cavity, as well as the coupler for the surface-normal output with a circular symmetry. Fabrication of the device entailed two epitaxial steps. Metallo-organic vapour phase epitaxy MOVPE was first used to grow the GaInAsPInP DH in the standard way. Circular mesas were then formed with reactive ion etching RIE to a depth just past the active layer. Regrowth of the waveguiding region followed, after which contacts were evaporated to the central mesa and the n-type InP substrate. Focused ion beam FIB was used to pattern the DBR circular grating in PMMA with a length of 140 micrometers and period of 0.4 micrometers. Using this resultant mask the grating pattern was transferred to the guiding layer by CH4H2 RIE to a depth of 0.2 micrometers. A scanning electron micrograph of a finished device is presented.