Showing papers on "Heterojunction published in 1969"

Low‐work‐function surfaces for negative‐electron‐affinity photoemitters

Abstract: The photoemission threshold of GaAs–Cs–O is explained on the basis of a heterojunction model composed of GaAs and Cs2O. The concepts involved in this model are generalized to an arbitrary heterojunction, leading to the result that it is, in principle, possible to obtain surfaces with work function lower than 0.5 eV. If deposited on an appropriate substrate, these surfaces offer the exciting possibility of highly efficient photoemission well into the infrared. A possible practical negative‐electron‐affinity photoemitter with efficient response to 1.4 μ is suggested.

The realization of a GaAs—Ge wide band gap emitter transistor

Abstract: The fabrication and properties of an n-GaAs emitter, p-Ge base, n-Ge collector transistor which possesses significant current gain is described, These GaAs wide band gap emitter transistors have shown incremental current gains near 15 when operated at current densities up to 3500 A/cm2. The doping level used in the base region was quite high (up to 5×1019/cm3in order to avoid a spurious Ge p-n junction in this region. The epitaxial deposition of the GaAs emitter region was carried out at a low temperature in order to also avoid a hidden p-n Ge junction. The low deposition temperature resulted in low (about 5×1015/cm3emitter doping levels. The general nature of the GaAs-Ge heterojunction energy-band diagram permits this high doping in the base or Ge region relative to the GaAs emitter region without reducing the current gain below unity. The observation of gain in this n-p-n heterojunction structure where the emitter is much more lightly doped than the base is considered to be confirmation of the theoretical proposals of Shockley and Kroemer.

Stresses in Heteroepitaxial Layers: GaAs1−xPx on GaAs

Abstract: A model is presented showing that there is a previously unrecognized source of stress in epitaxially grown heterojunction structures, specifically caused by a set of inclined dislocations formed by misfit dislocations which turn upwards at the heterojunction. This stress is indirectly related to the lattice mismatch at the heterojunction. For small lattice mismatch, the inclined dislocations are in an ordered array and cause the layer to bend upon removal from the substrate. For large lattice mismatch, the inclined dislocations are random so that there are only localized stresses and no net bending stress. A series of heterojunctions of GaAs1−xPx vapor grown onto GaAs were prepared, and the GaAs1−xPx constant‐composition layers were removed from the substrate. The bending of the layers observed and the dislocation morphologies revealed in the layers by transmission electron microscopy, demonstrate the validity of the above model. In GaAs0.8P0.2 grown on GaAs, the stress due to lattice mismatch exceeds tha...

IMPROVED RED AND INFRARED LIGHT EMITTING AlxGa1−xAs LASER DIODES USING THE CLOSE‐CONFINEMENT STRUCTURE

Abstract: AlxGa1−xAs injection lasers have been fabricated over the compositional range in which the alloy has a direct bandgap transition (0 < x ≤ 0.34). At 300°K the threshold current density increases with x from 12 000 A/cm2 (λL = 8600 A) to 56 000 A/cm2 (λL = 7340 A) in uncoated devices with cavity lengths of about 10 mils. In the same range of x the external differential quantum efficiency gradually decreases from 40 to 16%. These are the highest efficiencies and lowest threshold current densities ever reported for room‐temperature lasers emitting in the same spectral range. The improvement is due to utilization of the new p+‐p heterojunction structure previously used by the authors in GaAs lasers to sharply reduce the internal optical loss by improving the optical confinement and reducing the absorption coefficient in the p+ material adjoining the active region. At 77°K lasing has been achieved to 6450 A and cw operation to 6900 A with the emission of 0.4 W per diode.

Efficiency calculations of heterojunction solar energy converters

Abstract: A theoretical evaluation of the maximum attainable solar conversion efficiencies of p-n and n-p heterodiodes is presented. The calculations are made for some of the theoretically efficient and feasible heterojunctions of IV and III-V group semiconductors. In these calculations, the Anderson diffusion model is used and carrier concentrations of the two semiconductors are so chosen that photo-carriers generated do not have to surmount any junction barrier. The calculated efficiencies are compared with the reported experimental values and with the conventional Si photovoltaic cell.

ZnTe-InAs heterojunctions

Abstract: Fabrication and electrical properties of p-ZnTe/n-InAs heterojunctions obtained by interface alloying, suggesting p-i-n structure from characteristics and capacitance behavior

The heterode strain sensor: An evaporated heterojunction device

Abstract: A new type of strain sensor has been demonstrated in the laboratory. The basic device is a p-n heterojunction diode that is fabricated by vacuum evaporation techniques directly onto a flexible substrate. Its two important properties are 1) its mechanical input characteristics are determined by the flexible substrate used in fabricating the heterojunction and 2) it functions as a low-output-impedance voltage source modulated by the substrate surface strain. The heterojunction combination that has been most commonly used is CdSe on Se. Typical devices exhibit a voltage/strain sensitivity of 500 volts per unit strain, with a differential resistance of 100 ohms, when biased at 5 mA. This corresponds to a "gauge factor" of 1000 for the diode strain sensor. Thus far, the substrates used have ranged in mechanical properties from 2-mil-thick plastic to 40 mil microscope slides but the most useful substrate appears to be anodized Al. This device is still under active experimental study. Thus the characteristics cited in this paper are preliminary in nature, and represent the current research status of this strain sensor.

Heteroepitaxial growth of ZnS on GaP

Abstract: Epitaxial layers of ZnS were grown on GaP single crystals by a chemical transport reaction. The growth process and the heterostructures obtained were investigated by X-ray diffraction and optical microscopy. It was found that the epitaxial overgrowth is polarity dependent. The formation of a transition layer at the interface between the ZnS and GaP was observed.

The effect of a field-independent polarization discontinuity on heterojunction characteristics

Abstract: A new utilization of the basic semiconductor heterojunction is proposed which is based on the mechanism of a field-independent polarization discontinuity P at the interface of a p-n heterojunction. Variations in P yield changes in the space-charge regions and the associated barrier voltages at the interface. By proper choice of the heterojunction parameters, the barrier voltage change can be made approximately linear with P over a finite range. The barrier voltage variation modulates the I-V characteristic of the heterojunction for the case of a positive reverse interface barrier, and modifies the C-V relation in all cases. Typical values are calculated for the properties of the general polarization discontinuity heterojunction, and of a strain-sensitive unit which utilizes a piezo-electric interaction. For the latter, the calculated differential sensitivities are 102to 103and 104to 105volts per unit strain for the barrier voltage and device output voltage, respectively. This output voltage sensitivity is 1 to 2 orders of magnitude larger than that available in piezoresistive strain gages. This device concept has potential in a variety of technically important areas ranging from mechanical instrumentation to sequentially excited light-emitting arrays. The heterojunction configuration is compatible with both evaporated and epitaxial semiconductor technology, and materials with the necessary combination of physical properties are represented among the well-known II-VI and III-V compounds.

Device employing selenium-semiconductor heterojunction

Abstract: A semiconductor device comprising contiguous layers of crystalline selenium and cadmium selenide with a P-N heterojunction therebetween disposed on a high work function electrode. A thin tellurium film is disposed between the electrode and the selenium layer, and acts as a buffer to provide compatibility between the selenium crystalline structure and the structure of the underlaying electrode. When employed as a stress-sensitive transducer, the device is disposed on a flexible substrate. The device may also be employed as a thin-film diode.

An infrared sensitive Ge-Te heterojunction

Abstract: A new Ge-Te heterojunction device is described. Its small-signal-level resistance under IR excitation can be smaller than its dark resistance by a factor of at least 1000 at 77 K.

An evaporated heterojunction diode strain sensor

Abstract: Using a new device concept, a unique semiconductor strain sensor has been demonstrated in the laboratory. It is a p-n heterojunction diode which is fabricated by vacuum evaporation techniques directly onto flexible substrate. This sensor's mechanical input properties are controlled by the choice of substrate, and it has a low-impedance voltage source output characteristic.

Ge-Si n-n Heterojunctions

Abstract: Ge-Si n-n heterojunctions have been fabricated by epitaxial vapour growth process of hydrogen reduction of germanium tetrachloride. They have a good rectification property and a short switching time less than a few nano-seconds. In the junction there exists a double Schottky barrier due to interface states, which capture electrons more than 1.5×1013 cm-2 as acceptor-like states. The voltage-current characteristics have been measured at temperatures between 77°K and 300°K. In the low voltage region of easy flow direction (Germanium positively biased), d(log I)/dV is independent of temperature, but in the higher voltage region it is proportional to q/kT. The reverse characteristics (Germanium negatively biased) are divided into three separate regions, which are I∝V0.7~0.8, I∝V3/2 and I∝exp (BV) in the order of magnitude of reverse bias voltage, where B is a constant depending on temperature and donor concentration of silicon. The conduction mechanisms of this heterojunction have been discussed qualitatively.

Avalanche luminescence in CdS-Te heterojunctions

Abstract: Edge luminescence has been observed at 77 K in CdS-Te heterojunctions. Emission spectra, I-V curves, barrier heights, luminescent threshold, and saturation values are reported.

Diffused heterojunction multilayer coatings for electrostatic photography

Abstract: A method of coating surfaces for electrostatic photography which consists in successively depositing dissimilar materials on to a surface under conditions such that partial diffusion of one material into the adjacent material occurs at the interface between the dissimilar materials to an extent such that zones of p-type and n-type semiconductors are produced in the diffused region which act together as rectifying junctions to allow control of holes and electrons produced by photons which enter such an area, the first layer preferably being a conductor or semiconductor and the second layer being a photoconductor or an insulator with some injected charge mobility.

Energy Band Structure of Semiconductors

Abstract: During the past three years we have developed greatly improved methods for determining the electronic energy band structure of crystals. In the course of perfecting these methods, we investigated the electronic band structure and related physical properties of over 50 crystalline solids, including the diamond-type crystals; various polytypes of SiC; a large number of III–V, II–VI, and I–VII compounds having the sphalerite structure; additional II–VI and I–VII crystals having the wurtzite and rock-salt structures; several II–IV compounds (anti-fluorite structure); a number of IV–VI compounds (rock-salt structure); and various solid rare gases (face-centered cubic structure). Most of the substances studied were semiconductors with band gaps in the range from 0.5 to 5 eV; some were small band-gap semiconductors or semi-metals; the others were insulators with band gaps larger than 5 eV. All these materials are of scientific interest; many, especially Si, Ge, SiC, and various III–V, II–VI, and IV–VI compounds, are also of considerable technological interest.

Impurity profile and energy band diagram for the cuprous sulfide-cadmium sulfide heterojunction

Abstract: Impurity profile and energy band diagram for cuprous sulfide-cadmium sulfide heterojunction

Semiconductor heterojunction device

Abstract: A semiconductor device including a semiconductor body having at least one junction between two semiconductor compounds which consist of same two elements, for example tin selenide and tin diselenide.