At&t Bell Laboratories

Li-Wei Tu

George J Zydzik

Erdmann F Schubert

Alfred Yi Cho

Henry M O'Bryan, Jr

Dennis G Deppe

Niloy K Dutta

Rose F Kopf

Yeong-Her Wang

This invention embodies a LED in which an optical cavity of the LED, which includes an active layer (or region) and confining layers, is within a resonant Fabry-Perot cavity. The LED with the resonant cavity, hereinafter called Resonant Cavity LED or RCLED, has a higher spectral purity and higher light emission intensity relative to conventional LEDs. The Fabry-Perot cavity is formed by a highly reflective multilayer distributed Bragg reflector (DBR) mirror (R.sub.B .gtoreq.0.99) and a mirror with a low to moderate reflectivity (R.sub.T .perspectiveto.0.25-0.99). The DBR mirror, placed in the RCLED structure between the substrate and the confining bottom layer, is used as a bottom mirror. Presence of the less reflective top mirror above the active region leads to an unexpected improvement in directional light emission characteristics. The use of a Fabry-Perot resonant cavity formed by these two mirrors results in optical spontaneous light emission from the active region, which is restricted to the modes of the cavity. While the bottom DBR mirror reduces absorption by the substrate of that light portion which is emitted toward the substrate, the two mirrors of the resonant cavity reduce the isotropic emission and improve the light emission characteristics in terms of a more directed (anisotropic) emission.

Light emitting diode

This invention embodies a Vertical Cavity Surface Emitting Laser with a top mirror comprising at least one pair of quarterwave layers, each pair consisting of a low index of refraction layer and a high index of refraction layer, the high index of refraction layer being a semiconductor chosen from GaP and ZnS and the low index of refraction layer being chosen from borosilicate glass (BSG) CaF.sub.2,MgF.sub.2 and NaF. Especially useful in vertical cavity surface emitting lasers are mirrors formed by a stack of a plurality of pairs of GaP/BSG or ZnS/CdF.sub.2. Such mirrors have a high reflectivity characteristics required for an efficient operation of the laser. The GaP/BSG or ZnS/CaF.sub.2 mirror structure represents a considerable improvement over previous designs for VCSELs in terms of ultimate reflectivity, low loss, and post growth processing compatibility.

Optical devices with electron-beam evaporated multilayer mirror

Conduction band or valence band discontinuities occurring at the junction of two unipolar heterogeneous semiconductors can be eliminated by compositional grading of the heterointerface and appropriate doping of the interfacial region. The compositional potential of graded junction and an interface dipole potential generated by modulation doping of the interfacial region are selected such that they exactly compensate each other. The compositional grading of the interface is achieved by semiparabolic grading of narrow regions immediately adjacent each side of the interface. The modulation doping is achieved by doping the two materials with suitable dopants, donors for the conductance band or acceptors for the valence band, depending on the polarity of the structure. This reduces the resistance in periodic semiconductor multilayer structures leading to low-resistance distributed Bragg reflectors.

Elimination of heterojunction band discontinuities

Optically transparent and electrically conductive cadmium tin oxide or indium tin oxide is employed in vertical cavity surface emitting lasers for vertical current injection. Continuous wave lasing at room temperature is achieved in GaAs/AlGaAs quantum well lasers. Devices with a 10 .mu.m optical window which also serves as a vertical current injection inlet give lasing threshold currents as low as 3.8 mA. The differential series resistance is (350-450) .OMEGA. with a diode voltage of (5.1-5.6) V at the lasing threshold. Far field pattern of the laser emission is Gaussian-like with a full width at half maximum of 7.degree..

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Westfield, NJ, United States of America

Li-Wei Tu