At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Lucent Technologies Inc.

At+t Corp.

American Telephone and Telegraph, Co.

Erdmann F Schubert

George J Zydzik

John E Cunningham

Neil E Hunt

Rose F Kopf

Li-Wei Tu

Won-Tien Tsang

Alastair M Glass

Dennis G Deppe

John Milo Poate

Leonard C Feldman

Niloy K Dutta

Matthias Passlack

Alfred Yi Cho

Yiu-Huen Wong

Timothy D Harris

Henry M O'Bryan, Jr

Russell Dean Dupuis

Dale C Jacobson

Jan P Van Der Ziel

Stephen W Downey

Adrian B Emerson

Russell J Fischer

Yeong-Her Wang

J M Kuo

Henry S Luftman

Arjen M Vredenberg

Li Wei Tu

An optoelectronic lII-V or II-VI semiconductor device comprises a thin film coating with optical characteristics providing low midgap interface state density. A field effect device for inversion channel applications on III-V semiconductors also comprises a thin dielectric film providing required interface characteristics. The thin film is also applicable to passivation of states on exposed surfaces of electronic III-V devices. The thin film comprises a uniform, homogeneous, dense, stoichiometric gallium oxide (Ga.sub.2 O.sub.3) dielectric thin film, fabricated by electron-beam evaporation of a single crystal, high purity Gd.sub.3 Ga.sub.5 O.sub.12 complex compound on semiconductor substrates kept at temperatures ranging from 40.degree. to 370.degree. C. and at background pressures at or above 1.times.10.sup.-10 Torr.

Gallium oxide coatings for optoelectronic devices using electron beam

Disclosed is a method of fabricating a stoichiometric gallium oxide (Ga.sub.2 O.sub.3) thin film with dielectric properties on at least a portion of a semiconducting, insulating or metallic substrate. The method comprises electron-beam evaporation of single crystal, high purity Gd.sub.3 Ga.sub.5 O.sub.12 complex compound combining relatively ionic oxide, such as Gd.sub.2 O.sub.3, with the more covalent oxide Ga.sub.2 O.sub.3 such as to deposit a uniform, homogeneous, dense Ga.sub.2 O.sub.3 thin film with dielectric properties on a variety of said substrates, the semiconducting substrates including III-V and II-VI compound semiconductors.

Electron beam deposition of gallium oxide thin films using a single high

Absorption properties of an optically active medium can be changed drastically by a Fabry-Perot microcavity. Optically active medium of the cavity includes a host material which is not optically active and at least one rare earth ion which provides optical activity to the medium. The Fabry-Perot cavity is designed to be resonant with excitation wavelength of an absorption band of the host material. The excitation is provided by a source of radiation positioned such that the radiation impinges on the cavity at an angle within a range of from zero to less than 90 degrees from the normal to the top surface of the cavity. In one embodiment Er-implanted SiO.sub.2 is used as the optically active medium. SiO.sub.2 :Er has an absorption band at 980 nm and an emission band at 1.55 .mu.m due to 4f intra-atomic transitions of Er.sup.3+ ions. The Fabry-Perot cavity is designed to be resonant with the 980 nm absorption band of SiO.sub.2 :Er. The efficiency of the cavity structure is much higher as compared to a no-cavity structure, while the spectral features of the active SiO.sub.2 :Er emission are unaltered. The structure can be used for optically pumped semiconductor devices, such as optical amplifiers or lasers, which could be operated with a higher overall efficiency.

Absorption resonant rare earth-doped micro-cavities

This invention embodies single mirror light-emitting diodes (LEDs) with enhanced intensity. The LEDs are Group III-V and/or II-IV compound semiconductor structures with a single metallic mirror. The enhanced intensity is obtained by placing an active region of the LED having from two to ten, preferably from four to eight, quantum wells at an anti-node of the optical node of the device created by a nearby metallic mirror. Such multiquantum well LED structures exhibit enhanced efficiencies approaching that of a perfect isotropic emitter.

Single mirror light-emitting diodes with enhanced intensity

Described is a resonant-cavity p-i-n photodetector based on the reflection or transmission through a Fabry-Perot cavity incorporating non-epitaxial, amorphous layers with alternating refractive index difference which layers are electron-beam deposited on a light-gathering side of a commercially available photodetector. The materials of the Fabry-Perot cavity are selectable from materials, refractive indices of which fall within a large range (from n=1.26 for CaF.sub.2 to n=3.5 for Si) preferably from materials which are depositable in an amorphous state. The material combinations are selected so that only wavelengths resonant with the cavity mode will be detected. The microcavity of the RC-PIN design can also be deposited on any existing detector structure, without modification of semiconductor growth. Such a photodetector would be useful for wavelength de-multiplexing applications. The ease of layer deposition, as well as the high degree of tailorability of spectral position, spectral detection width, and maximum numerical aperture of efficient detection, make the RC-PIN attractive for use in wavelength demultiplexing applications. An exemplary RC-PIN photodetector includes a Si/SiO.sub.2 Fabry-Perot cavity electron-beam deposited on the InP substrate of a commercial InGaAs photodetector. The detection efficiency relative to a reference device was 52 percent at the resonant wavelength of 1350 nm, with a resonance width of 14 nm, and a 4 percent response for off-resonance wavelengths in the 1100-1700 nm range.

Photodetector with a resonant cavity

This invention embodies p-n junction devices comprising Group III-V compound semiconductors in which the p or n or both p and n regions are formed by a superlattice selectively doped with an amphoteric Group IV element dopant selected from carbon, germanium and silicone. The superlattice includes a plurality of periods, each including two layers. Depending on the conductivity type, only one of the layers in the periods forming the superlattice region of said type of conductivity is selectively doped with said dopant, leaving the other layer in these periods undoped. The superlattice is formed by Molecular Beam Epitaxy technique, and the dopant is incorporated into respective layers by delta-doping as in a sheet centrally deposited between monolayers forming the respective layers of the period. Each period includes 5 to 15 monolayers deposited in the two layers in a numerical ratio corresponding to a cation compositional ratio in the compound semiconductor. Low growth temperatures, e.g. ranging from 410.degree. to 450.degree. C. lead to mirror-like surfaces. For a compound semiconductor Ga.sub.0.47 In.sub.0.53 As, the GaAs/InAs ordered superlattices with eight monolayers per period are grown in a ratio of 0.47/0.53. At free carrier concentrations of 10.sup.16 cm.sup. -3, carrier mobilities of 200 and 2300 cm.sup.2 /Vs for p-type and n-type are obtained with carbon as the amphoteric dopant.

P-N junction devices with group IV element-doped group III-V compound

This invention embodies an optical device with a Fabry-Perot cavity formed by two reflective mirrors and an active layer which is doped with a rare earth element selected from lanthanide series elements with number 57 through 71. The thickness of the active layer being a whole number multiple of .lambda./2 wherein .lambda. is the operating, or emissive, wavelength of the device, said whole number being one of the numbers ranging from 1 to 5, the fundamental mode of the cavity being in resonance with the emission wavelength of said selected rare earth element. Cavity-quality factors exceeding Q=300 and finesses of 73 are achieved with structures consisting of two Si/SiO.sub.2 distributed Bragg reflector (DBR) mirrors and an Er-implanted (.lambda./2) SiO.sub.2 active region. The bottom DBR mirror consists of four pairs and the upper DBR mirror consists of two-and-a half pairs of quarterwave (.lambda./4) layers of Si and SiO.sub.2. Photoluminescence at room temperature reveals a drastic enhancement of the luminescence intensity of the cavity emitted along the optical axis of the cavity versus the luminescence without the top mirror. The luminescence intensity of the cavity is typically 1-2 orders of magnitudes higher as compared to structures without a cavity. Furthermore, since the emission wavelength and the intensity decrease for off-normal emission angles, the change in emission wavelength can be quantitatively described by assuming that the on-axis component of the optical wave is resonant with the cavity.

Erbium doped optical devices

It has been found that in the preparation of devices having repetitive layers, such as distributed Bragg reflectors, the dopant introduced during processing redistributes itself in a deleterious manner. In particular, this dopant through various effects segregates and diffuses from one layer into the interface region of the second layer. As a result, properties such as electrical resistance of the structure become unacceptably high. By utilizing various expedients such as carbon doping this segregation and its associated deleterious effects are avoided.

Devices having repetitive layers

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..

Vertical cavity surface emmitting lasers with transparent electrodes

This invention is a semiconductor vertical cavity surface emitting laser comprising a lasing cavity with an active layer, a bottom (rear) mirror and a top (front) mirror, and a front and rear electrodes for applying excitation current in direction substantially parallel to the direction of optical propagation. In accordance with this invention the front mirror comprises a thin, semitransparent metal layer which also acts as the front electrode. The metal layer is upon a highly doped layer forming a non-alloyed ohmic contact. The metal is selected from Ag and Al and is deposited in thickness ranging from 5 to 55 nm. The VCSEL is a semiconductor device wherein the semiconductor material is a III-V or II-VI compound semiconductor. For a VCSEL with GaAs active layer, the light output from the front metal mirror/electrode side yields a high external differential quantum efficiency as high as 54 percent. This is the highest quantum efficiency obtained in VCSEL structures. Quantum efficiencies on the oder of 10 to 30 percent are typical for prior art VCSEL structures. The VCSEL is suitable for fabrication utilizing planar technology.

Vertical cavity surface emitting lasers with electrically conducting

The use of alternating n and p type regions asymmetrically spaced in a semiconductor material yields extremely advantageous properties. In particular, by controlling the doping level and the spatial configuration of the doped region both the device response and its optical properties are controllable. Therefore, in applications such as those involving optical switches LEDs, lasers and long wavelength detectors, both the speed of device and its optical properties are controllable. As a result, greater fabrication flexibility than previously available is possible.

Devices having asymmetric delta-doping

A process is described for making semiconductor devices with highly controlled doping profiles. The process involves minimizing or eliminating segregation effects caused by surface electric fields created by Fermi-level pinning. These electric fields act on dopant ions and cause migration from the original deposition site of the doplant ions. Dopant ions are effectively shielded from the surface electric fields by illumination of the growth surfaces and by background doping. Also, certain crystallographic directions in certain semiconductors do not show Fermi-level pinning and lower growth temperatures retard or eliminate segregation effects. Devices are described which exhibit enhanced characteristics with highly accurate and other very narrow doping profiles.

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New Providence, NJ, United States of America

Erdmann F Schubert