GB1288082A - - Google Patents

Abstract

1288082 Electroluminescence WESTERN ELECTRIC CO Inc 10 Oct 1969 [11 Oct 1968 27 Dec 1968] 49780/69 Heading C4S [Also in Division H1] A semi-conductor injection laser operable continuously at room temperature comprises two portions of semi-conducting material 12, 14, Fig. 1, the latter having a narrower band gap than the former and containing a P-N juncton 25 spaced from the phase boundary 23 between the portions by a distance less than the minority carrier diffusion-length. The narrower band width portion 14 may be GaAs, the N-type region being Sn doped and the P-type intermediate zone 24 Zn doped, while the wider band gap portion 12 may be Al x Ga 1-x As or GaAs 1-x P x which is rendered P-type by Zn doping. Pumping current is supplied from generator 18 via electrodes 20, 22, which may be of Ti/Au and Sn/Ni respectively, and heat is extracted by sink 16. Faces 28 and 30 are flat and may have a reflective coating, while faces 32 and 34 may be roughened or polished depending on the required cavity Q. Reflective faces with stripe patterns may be used for mode selection. In operation, the phase boundary confines injected electrons to the intermediate zone 24 because of the change of band gap across the boundary, thus lowering the lasing threshold current. The output in this embodiment is thus from the intermediate zone. In order to reduce the dependance of threshold current on temperature, deep states may be created near the conduction or valence bands. For example if deep acceptor states are provided in the intermediate and/or narrower band gap regions, Fig. 2B, e.g. by doping with Mn, Co, Ni, Cu or Al, lasing occurs in the doped regions by recombination of electrons in the conduction band with holes injected into the deep states from the valence band. Output is typically 9500 Š at room temperature, with a threshold current of 10,000 amps/cm.<SP>2</SP>. Deep states may be provided near the conduction and valence bands by creating tails on these bands, Fig. 4C, by heavy doping. 10<SP>19</SP>/cm.<SP>3</SP> of Si, Ge or Sn gives tails on both bands, while Te produces a tail on the conduction band alone and Zn a tail only on the valence band. Best tail formation is stated to be possible with a laser having P-type GaAs as the wider band gap material, and N-type In x Ga 1-x As or GaAs 1-x Sb x as the narrower gap material. Alternative lasers based upon InP, InAs or InSb are stated to be possible.