GB1461869A - Semiconductor laser device - Google Patents

Abstract

1461869 Semi-conductor lasers HITACHI Ltd 26 Sept 1974 [5 Oct 1973] 41947/74 Headings H1C and H1K [Also in Division C4] The functional equivalent of a resonator of a semi-conductor laser is produced by distributed feedback from a periodically corrugated optical confinement boundary 4 extending parallel to the laser active layer 2. In Fig. 1, the laser comprises an N-type GaAs layer 1, a P-type GaAs active layer 2, a P-type Ga 0.9 Al 0.1 As layer 3 having a periodically corrugated surface 4, and a P-type Ga 0.6 Al 0.4 As layer 5, the refractive index of layer 5 being less than that of layer 3. Electrodes 6, 7 formed of chromium and gold, and gold containing germanium and nickel, respectively, are provided on the outermost layers. To produce laser radiation of 8750 Š wavelength the corrugation period should be 0À123 Ám and the corrugation depth 500 Š. In a modification requiring a lower threshold current for laser oscillation a further layer 8, Fig. 2, of N-type Ga 0À7 Al 0À3 As, or two additional layers 8 and 10, Fig. 3, of N-type Ga 0À6 Al 0À4 As and P-type Ga 0À9 Al 0À1 As, respectively, are provided between the layers 1 and 2. In a modification of Fig. 3 the boundary 11, Fig. 4, between the layers 8 and 10 is also periodically corrugated. The layered assembly is produced by liquid phase epitaxial growth, the manufacturing step involving the periodic corrugations involving coating layer 3 or 8 with photoresist which is then exposed to ultra-violet light to form interference fringes. After development of the photoresist the layer surface is milled into corrugations by ion etching. For layers 3 and 8 the composition may be changed to the extent of Ga 0À8 Al 0À2 As. Alternative lasing materials are Suitable P-type dopants are stated to be silicon, tellurium and zinc.