Showing papers on "Heterojunction published in 1970"

Behavior of Cesium Oxide as a Low Work‐Function Coating

Abstract: A detailed picture of the behavior of cesium oxide as a low work‐function coating on III‐V semiconductors and on silver has been obtained. Measurement of required cesium and oxygen exposure for optimum photoyield shows that the compound normally formed is close to CS2O, with variations in required exposure for very thin and very thick layers. By making simultaneous Kelvin work‐function, photoyield‐threshold, and thickness measurements, it was possible to establish that the CS2O, an n‐type semiconductor, forms a heterojunction or Schottky barrier with its substrate. This provides a band bending which produces a gradual lowering of the vacuum level with increasing thickness to an ultimate work function of 0.6 eV. The photoyield and dark current from the substrate are limited by the interfacial barrier at the heterojunction. This barrier is 1.00±0.05 eV for a silver substrate and 1.23±0.03 eV for GaSb. The band‐bending distance in the CS2O is about 50 A and the hot electron scattering distance is 9 A. These data have been used in an improved calculation of the maximum Γ escape probability and requisite CS2O thickness for electron emission from III‐V semiconductors of different bandgaps. Electron emission from CS2O induced by an oxygen overpressure was also measured. CSOH is compared with CS2O as a work‐function lowering coating.

GaAs–GaxAl1−xAs Heterostructure Injection Lasers which Exhibit Low Thresholds at Room Temperature

Abstract: The electrical and optical properties of GaAs–GaxAl1−xAs injection lasers produced by solution epitaxy are described. These lasers are composed of three layers, n‐GaAs, a thin p‐GaAs layer, and a p‐GaxAl1−xAs layer. In these lasers, the threshold current Jth is a strong function of the width of the p‐GaAs layer d, being optimum where d is about 2 μ. The temperature dependence of Jth is comparatively small below some maximum temperature TM, above which it increases very rapidly. The values of Jth obtained near room temperature for these lasers are lower than have previously been reported for injection lasers. Fabry‐Perot‐type diodes with cavities of about 400 μ may be reproducibly prepared with Jth (300°K) about 10 000 A/cm2. The lowest Jth (300°K) observed for one of these units was 8600 A/cm2. Units with fully internally reflected modes can be reproducibly prepared with Jth (300°K) ≈6000–7000 A/cm2. The low Jth (300°K) of these lasers is attributed primarily to carrier confinement, although improved opti...

Control of Optical Losses in p‐n Junction Lasers by Use of a Heterojunction: Theory and Experiment

Abstract: The optical losses of homojunction and heterojunction ``close‐confinement'' GaAs injection lasers fabricated by liquid phase epitaxy have been described in terms of a simple waveguide model. By introducing an (AlGa) As–GaAs p+‐p heterojunction (ΔEg∼0.1 eV) within ∼2 μ of the p‐n junction, the room‐temperature absorption loss is substantially reduced and the laser efficiency increased. This reduced absorption is due to combination of improved optical waveguiding and reduced absorption in the p+ material adjoining the active region. In addition, the laser gain coefficient can be increased in some cases by the addition of a heterojunction with the degree of improvement depending on the electron diffusion length, width, and doping level of the active region. The increased gain coefficient can contribute substantially to the reduced threshold current density of ``close‐confinement'' lasers at room temperature. However, the relative contributions of reduced laser loss and increased gain coefficient to the impro...

Electrical and Optical Properties of Si-SnO 2 Heterojunctions

Abstract: Electrical and optical properties have been investigated on Si–SnO2 heterojunctions. Semiconducting SnO2 film has been grown by a successive oxidation of the evaporated tin on the (111) surface of silicon single crystal. The SnO2 film shows the properties of a degenerate n-type semiconductor having the band gap energy of 3.5 eV. The current-voltage characteristics of Si–SnO2n–n heterojunction represent a good rectification. The photovoltage measurements demonstrate that the Si–SnO2n–n heterojunction has the photoresponse in the wide wavelength region from 400 to 1200 mµ at room temperature. The energy band diagram of Si–SnO2n–n heterojunction is determined from the results of these electrical and optical measurements.

Heterojunction solar cell calculations

Abstract: Collection efficiency and spectral response calculations for semiconductor heterojunction solar cells

AlxGa1−xAs1−y′P y′–GaAs1−yPy HETEROSTRUCTURE LASER AND LAMP JUNCTIONS

Abstract: A method is described to grow successfully from solution AlxGa1−xAs1−y′P y′ (p‐type) on GaAs1−yPy (n‐type), to preserve the lattice match (y′ ≈ y), and to obtain the improved heterostructure junction devices previously realized only in the AlGaAs/GaAs system. Although not optimized, these structures have been operated as pulsed room‐temperature lasers, and because of an inherent wide‐gap window can be used conveniently for optical purposes and for excess carrier lifetime measurements. Carrier lifetime measurements, for example, indicate freedom from defects at the AlGaAsP/GaAsP barrier.

FABRY‐PEROT STRUCTURE AlxGa1−xAs INJECTION LASERS WITH ROOM‐TEMPERATURE THRESHOLD CURRENT DENSITIES OF 2530 A/cm2

Abstract: Heterojunction injection lasers of (AlGa) As have been made with room‐temperature threshold current densities ∼3 times lower than previously reported devices emitting in the same spectral range. Fabry‐Perot structure lasers with Jth as low as 2530 A/cm2 emitting at ∼8800 A are described. The improved performance is partly due to a very high optical gain coefficient resulting from a high doping level in an exceptionally narrow lasing region (0.8μ).

Double heterostructure junction lasers

Abstract: A light emitting heterostructure diode includes a multilayered structure having a common conductivity type heterojunction and a p-n junction separated therefrom by a distance less than the diffusion length of minority carriers, thereby defining an intermediate region bounded by said junctions.

Performance potential of high-frequency heterojunction transistors

Abstract: Assuming a state-of-the-art microwave planar geometry, the maximum frequency of oscillation has been calculated for GaAs-Ge heterojunction transistors utilizing either doped or high-resistivity space-charge-limited emitters. This is compared with a Ge homojunction transistor of the same geometry. A detailed equivalent circuit is used which accounts for the parasitics of the chip. It is shown that if chip parasitics are neglected, GaA-Ge devices should outperform Ge devices by about 4 to 1 in power gain. In the geometry assumed, however both heterojunction and homojunction transistors are limited by wafer parasitics, particularly base contact resistance. The calculated figures of merit of the two types of devices are therefore quite similar.

LONG‐WAVELENGTH THRESHOLD OF Cs2O‐COATED PHOTOEMITTERS

Abstract: While Cs2O‐coated III‐V semiconductors can have Kelvin work functions as low as 0.7 eV, the long‐wavelength threshold for efficient photoemission is determined by a significantly higher barrier at the heterojunction between the Cs2O and the semiconductor. This barrier is 1.23±0.03 eV for Cs2O on GaSb. For Cs2O on silver, the barrier height is 1.0 eV.

Gain and loss processes in GaAlAs-GaAs heterostructure lasers

Abstract: Heterostructure lasers have been made by growing an epitaxial p+layer of GaAlAs onto an n+-GaAs substrate. The p-GaAs active region, formed by diffusion of zinc into the substrate during the growth process, is about 1.6 μ thick. Threshold current densities of these lasers lie between 8000 and 12 000 A.cm-2at 300°K, depending on the cavity length. External incremental quantum efficiencies are about 40 percent and change very little with cavity length. It is found that the gain coefficient is a superlinear function of current and the loss coefficient appears to vary with cavity length as a result of the variation in photon energy, which occurs with different threshold currents. The threshold currents of the heterostructure lasers are a factor of 4 lower than previous homojunction lasers. The conclusion is drawn that the improvement is largely a result of the carrier confinement that occurs at the heterojunction. Some improvement can be related to a reduction of optical losses but it is a consequence of the superlinear gain-current relationship that even a loss coefficient of zero would be insufficient to explain the low-threshold currents.

AN OPTOELECTRONIC COLD CATHODE USING AN AlxGa1−xAs HETEROJUNCTION STRUCTURE

Abstract: An efficient optoelectronic cold cathode has been made which includes a Si‐compensated AlxGa1−xAs electroluminescent diode covered with an absorbing p‐type GaAs layer having a negative electron affinity surface. This structure is designed to minimize current crowding in the vicinity of the Ohmic contact. An over‐all efficiency of 1.1×10−3 (current emitted into vacuum/diode current) has been achieved. This represents a factor of 102–103 improvement over previous p‐n junction or optically coupled cold cathode structures.

Optical field distribution in close-confined laser structures

Abstract: An experimental and theoretical study has been made of the radiation patterns from GaAs lasers with a "close-confined" structure. The lasers were grown by liquid-phase epitaxy and consisted of a p+ - p-n structure with Al in the p+ region. Photometric measurements were made of the intensity distribution at the emitting facet (microscope observations) and the radiation pattern in a plane perpendicular to the junction. The electromagnetic field distribution in the vicinity of the p-n junction and the radiation pattern were calculated by solving the wave equation for a three-layer structure with complex dielectric constants in each layer. The theory predicts enhanced confinement of the radiation by the increased dielectric discontinuity due to the heterojunction, in agreement with the low lasing threshold and high efficiencies of the close-confined diodes. Another consequence of the theory is that as the thickness d of the p region of the cavity is increased, higher order modes can propagate with efficiences much greater than in ordinary lasers without the heterojunction. The third mode, corresponding to three intensity maxima along a line perpendicular to the junction, was observed for d = 5 \mu . The good agreement found between the observed and calculated radiation patterns indicates that confinement of the radiation by dielectric discontinuities is an important factor in explaining the low-threshold currents found in close-confined lasers.

Pyropolymeric semiconducting organic-refractory oxide material

Abstract: A semiconducting material comprising a carbonaceous pyropolymer formed on a refractory oxide having a surface area of from about 1 to about 500 square meters per gram. A refractory oxide is heated to at least about 400 DEG C. in an atmosphere containing an organic pyrolyzable substance. The semiconducting material has a conductivity at room temperature of from about 10 8 to about 100 inverse ohm-centimeters, and is used for electrical applications such as heterojunction transistors, field-effect transistors, thermoelements in thermoelectric generators and refrigerators and temperature sensing devices, and electrodes in electrochemical cells, charge and energy storage devices, memory devices, inductive elements, and a variety of other electrical applications.

GaAs junction lasers containing the amphoteric dopants Ge and Si

Abstract: Laser operation ofp-n junctions in GaAs doped with amphoteric impurities is demonstrated. The previous limitation to laser operation of such junctions caused by the broad spatial spread of the injected carriers (electrons), and their consequent low density at a given current level, can be overcome with a heterojunction reflecting barrier juxtaposed within a diffusion length of the junction. The effect of the barrier is great enough to allow significant stimulated emission to occur in GaAs (p-type GaAs : Ge and GaAs : Si) not previously lased in junction structures, and at current levels 10 × lower than those that have been previously inadequate.

High‐order transverse cavity modes in heterojunction diode lasers

Abstract: A refined theoretical model predicts the modal content in the plane perpendicular to the junction for heterojunction injection lasers. It gives good agreement with observed far‐field patterns. Because high‐order modes are favored, lasers with a wide optical cavity sandwiched between two heterojunctions have a beam width at least double that of single‐heterojunction lasers. In a thin cavity which supports but one mode, the increased confinement of the double heterojunction broadens the beam to about 40° at half‐power.

The emission spectra of p‐AlxGa1−xAs–n‐GaAs heterojunctions

Abstract: The emission spectra of p-AlxGa1−xAs-n-GaAs heterojunctions with Ge- and Zn-doped AlxGa1−xAs layers have been studied. The dependence of the emission peaks on current, voltage, and temperature are examined. The peak shift observed at all diodes and other spectral characteristics are discussed in terms of a diagonal tunneling mechanism and a band filling model involving acceptor state tails on the valence band of GaAs.

Room-temperature close-confinement GaAs laser with overall external quantum efficiency of 40 percent

Abstract: The most efficient room-temperature GaAs injection lasers have been made by use of the close-confinement (heterostructure) technique. Differential external quantum efficiency in excess of 50 percent was observed on lasers having threshold current densities as low as 8500 A/cm2.

Preparation of gap-si heterojunction by liquid phase epitaxy

Abstract: A SATURATED MOLTEN SOLUTION OF GAP AND SI IN A SITUABLE SOLVENT (PB,SN) WAS PREPARED. THE MOLTEN, SATURATED SOLUTION WAS BROUGHT INTO CONTACT WITH A SI SINGLE CRYSTAL SUBSTRATE AND COOLED, CAUSING THE GAP TO FORM AN EPITAXIAL LAYER ON THE SI SURFACE. THE CRYSTAL LATTICE STRUCTURE AND DIMENSIONS OF SI AND GAP CRYSTALS ARE VERY SIMILAR. THE PREFERRED PHYSICAL PROPERTIES OF THE SOLVENT ARE: A RELATIVELY HIGH SOLUBILITY FOR GAP; A RELATIVELY LOW SOLUBILITY FOR SI; AND A RELATIVELY LOW SOLUBILITY OF THE SELECTED SOLVENT IN THE EPITAXIALLY GROWN GAP.

Radiative recombination in heavily doped n‐AlxGa1_xAs‐p‐GaAs heterojunctions

Abstract: Heavily doped n-AlxGa1_xAs-p-GaAs heterojunctions prepared by liquid phase epitaxy have been investigated. At high bias (U > 1.40 V at 77 °K), the emission of the diodes for which the “tip” temperature has been 850 °C corresponds to a band-acceptor transition in GaAs. The emission spectrum of the diodes for which the “tip” temperature has been equal or higher than 870 °C shows the existence of a peak-shifting line. In order to explain the peculiarities of the emission spectra a “band filling” mechanism involving a conduction band tail formed as a consequence of the impurity interdiffusion is discussed.

Vacuum-deposited thin-film p-Se/n-CdSe heterojunction diodes

Abstract: A preliminary feasibility study has been made of vacuum-deposited thin-film diodes based on the p-Se/n-CdSe heterojunction system. These diodes have excellent rectification properties, including: 1) 70-volt reverse breakdown, 2) 105rectification ratio over a range of 25 volts, and 3) 0.5-volt forward offset voltage. The diodes have a "sandwich-cell" structure formed by depositing a CdSe layer onto a Crystallized layer of Se. This work is still in a preliminary stage. However, the results thus far suggest that these diodes may be suitable for use in thin-film integrated circuits for those specialized circuit applications which require only diodes, resistors, and/or capacitors.