Semiconductor Lasers with Doping Gradients in Optical Confinement Areas to Increase Laser Efficiency

Current semiconductor lasers are 45 to 50 percent efficient. Lowering the voltage needed for lasing to occur could increase the electrical-to-optical power conversion efficiency significantly. UW–Madison researchers have developed a highly efficient aluminum-free semiconductor light-emitting source that is particularly suited for high-power diode lasers of one-watt continuous wave (CW) output or higher. This device is grown on a semiconductor substrate and includes in transverse section an active region layer containing quantum wells where the laser light is generated; optical confinement layers on either side of the active region layer; and cladding layers one that is p-type doped and the other n-type doped outside the confinement layers. The layers on either side of the active region layer confine the light emitted by the laser to the active region. What makes this aluminum-free semiconductor device unique is the presence of a doping gradient in the layers surrounding the active region. Doping is heaviest in the confinement layers adjacent to the active region and quantum wells and decreases toward the cladding layers. This doping profile creates an electric field that significantly increases the transport speed of injected carriers (i.e. electrons and holes) thereby reducing the non-ohmic voltage drop across the core of the device and greatly increasing laser efficiency. In addition these doping profiles do not introduce a large free carrier absorption (FCA) penalty because the device is aluminum-free. Applications: 1) Telecommunications 2) Fiber optics 3) Laser pumping