Showing papers on "Heterojunction published in 1977"
TL;DR: In this article, the authors present a refined model for the prediction of the energy-band lineup at an abrupt semiconductor heterojunction, which is independent of the crystallographic orientation of the semiconductor.
Abstract: We present a refined model for the prediction of the energy-band lineup at an abrupt semiconductor heterojunction. The position of the energy bands with respect to the electrostatic potential is calculated by a self-consistent pseudopotential,for the bulk semiconductors. The lineup of the electrostatic potentials is then calculated from an ionic model in which the ionic charges are determined by the electronegativities of the atomic species. The resulting band lineups are independent of the crystallographic orientation of the heterojunction. They are also generally consistent with experimental data.
245 citations
TL;DR: In this paper, the relative location of the band-edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally, and a series of currentvoltage characteristics which change from rectifying to Ohmic as x and y are reduced.
Abstract: Smooth films of n‐In1−xGaxAs and p‐GaSb1−yAsy were grown by molecular beam epitaxy. As a function of the compositions, x and y, the lattice constants vary linearly while the energy gaps show a downward bowing. Abrupt heterojunctions made of these alloys with close lattice matching exhibit a series of current‐voltage characteristics which change from rectifying to Ohmic as x and y are reduced. The relative location of the band‐edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally.
180 citations
TL;DR: In this paper, the development and application of a variable composition solar cell computer analysis program is discussed, the basic device equations as used in the computer analysis are derived and the techniques used to model material parameter variations described.
Abstract: The development and application of a variable composition solar cell computer analysis program is discussed, The basic device equations as used in the computer analysis are derived and the techniques used to model material parameter variations described. Finally, the results of the computer analysis of several Al x Ga 1-x As and GaAs 1-x P x solar cell structures are presented along with a discussion of the effects of interface states and various composition and doping profiles on maximum solar cell efficiency. Interface states are found to be responsible for a severe reduction in the efficiency of GaAs 1-x P x cells, but do not significantly affect the behavior of Al x Ga 1-x As cells. The depth of the p-n junction below the wide bandgap window layer is a critical factor in determining the loss of minority carriers to interface recombination at the heterojunction.
172 citations
TL;DR: In this article, a simple method is proposed for studying heterojunctions and it is shown that a dipole barrier is induced when the charge neutrality points of both semiconductors do not coincide.
Abstract: A simple method is proposed for studying heterojunctions. First, it is shown that a dipole barrier is induced when the charge neutrality points of both semiconductors do not coincide. The interface is analysed including the effects of this dipole and the many-electron interaction. Good agreement is found with available information.
138 citations
TL;DR: In this paper, single crystal semiconductors were coated with n-type TiO~ by a chemical vapor deposition technique, and the electron and hole transfer properties across the heterojunction so produced were investigated.
Abstract: Single crystal semiconductors (n-Si, p-Si, n-GaAs, p-GaAs, n-GaP, n-In.P, and n-CdS) were coated with n-type TiO~ by a chemical vapor deposition technique, and the electron and hole transfer properties across the heterojunction so produced were investigated. The quality of the deposited TiO~ film depended upon several factors including temperature and substrate material. When high quality crack-free TiO2 coats were obtained on n-type substrates, the substrate was stabilized with no dissolution during the photo-oxidation of water. However, the oxidation was due o~y to the photoexcitation of the TiO~, and any holes produced in the substrate were not transferred through the TiO~ to the solution. The use of p-type substrates coated with TiO2 as photocathodes was limited by band-bending requirements at the p-n heterojunction and the TiO~-solution interface.
130 citations
TL;DR: In this paper, a consistent method of evaluating the photon recycling effects on both ηin and L, based on simultaneous measurements of the external quantum efficiency ηex and the photo-excited current under the short circuit condition is presented.
Abstract: The photon recycling process, ie, the excitation of electron-hole pairs by the reabsorption of luminescent light, has large effects on the determination of the minority carrier diffusion length L and the internal quantum efficiency ηin GaAs with a high quantum efficiency In this report, we show that the separate treatments of L and ηin cause the erroneous results for materials with high quantum efficiency We developed a consistent method of evaluating the photon recycling effects on both ηin and L, based on the simultaneous measurements of the external quantum efficiency ηex and the photo-excited current under the short circuit condition Isc This method was applied to the specimens with single heterestructure (p-AlxGa1-xAs-p-GaAs-n-GaAs) prepared by the liquid phase epitaxial (LPE) process
109 citations
TL;DR: The fabrication and characteristics of several vacuumdeposited photovoltaic heterojunctions involving ternary compounds (CuInSe2, CuInS2, and CuInTe2) and a binary compound (InP with Cds) are described in this paper.
Abstract: The fabrication and characteristics of several vacuum‐deposited photovoltaic heterojunctions involving ternary compounds (CuInSe2, CuInS2, and CuInTe2) and a binary compound (InP) with Cds are described. The light and dark IV characteristics, spectral response data, and cell parameters (fill factors, open‐circuit voltages, short circuit currents, efficiencies) are reported for the thin‐film solar cells.
109 citations
TL;DR: In this article, the In2O3 (tin-doped) n-type silicon heterojunction solar cell was made using a very simple, cheap, and quick method.
Abstract: We present results concerning In2O3 (tin‐doped) n‐type silicon heterojunction solar cell. The transparent and conductive In2O3 : Sn layer was made using a very simple, cheap, and quick method. Conversion efficiency up to 10% is reported. Typical parameters under AM1 simulated sunlight are open‐circuit photovoltage Voc=500 mV, short‐circuit photocurrent Isc=32 mA cm−2, and fill factors around 0.6–0.65.
99 citations
TL;DR: In this paper, the electron affinity of the SnO2 films was shown to be approximately 0.8 eV greater than the electron affinities of the Si, which is consistent with the electron-hole recombination in the transition region.
Abstract: Heterojunction solar cells (HJSC’s), fabricated by electron beam evaportaion of SnO2 films onto monocrystalline and polycrystalline Si substrates, show conversion efficiencies as high as 9.9%, fill factors of 0.64, and open circuit voltages of 525 mV under AMI simulated irradiation. The SnO2, an n-type semiconductor, acts as a transparent window to solar irradiation and as an antireflection coating of the Si, and it provides the band bending in the Si necessary for photovoltaic conversion. The SnO2 films, nominally 50 nm thick, have conductivities of the order of 103(Ω-cm)−1 so that the film makes a good electrical contact between the junction and the metallic front contacts. Measurements of C−2-V and I-V characteristics are consistent with heterojunction theory, and the data imply an electron affinity of the SnO2 of approximately 0.8 eV greater than the electron affinity of Si. This value limits the open circuit voltage of HJSC’s made on p-type substrates to values too small for useful photovoltaic conversion. The predominant dark current mechanism of units of n-type substrates at room temperature and forward bias in the range of 0.3−0.5 V is electron-hole recombination in the transition region. The experimentally determined activation energy is 0.51 eV, approximately Eg/2. At forward voltages below 0.3 V, multistep tunneling via interband states predominates. The photocurrent apparently depends on interface states through which the photogenerated holes in the Si recombine with electrons in the SnO2.
TL;DR: In this paper, five heterojunction systems, involving the II-VI compounds CdSe, CdTe, ZnSe, and ZnTe, have been prepared using the close-spaced vapor transport method.
Abstract: Five heterojunction systems, involving the II‐VI compounds CdSe, CdTe, ZnSe, and ZnTe, have been prepared using the close‐spaced vapor transport method. Current transport through these heterojunctions was found to be dominated by recombination at the interface. Using a collection function, introduced to describe the voltage dependence of the collection of photogenerated carriers, diffusion potentials were determined, and from them values of the electron affinity of CdSe (4.53 eV) and ZnTe (3.73 eV) relative to CdTe (4.28 eV).
TL;DR: In this paper, the effect of grain boundaries in thin films and heterojunction lattice mismatch is demonstrated by simple models in order to gain a perspective on the required film properties and cell conjunctions.
TL;DR: In this article, CdS films were used as photovoltaic detectors with an absolute quantum efficiency of 80% at a wavelength of 5800 A and a solar power conversion efficiency of 5% when they are exposed to the solar light whose intensity is 71 mW/cm2.
Abstract: p‐CuGaSe2/n‐CdS heterojunctions have been prepared by depositing CdS films on p‐type CuGaSe2 single crystals whose initial resistivity was 10−2 Ω cm and changed to 1 Ω cm after the CdS film deposition. The CdS films, which were grown by a multisources method, exhibit a room‐temperature resistivity of 0.1 Ω cm. The absolute quantum efficiency of these devices as photovoltaic detectors reaches the value of 80% at a wavelength of 5800 A. As solar cells, these heterojunctions at 25 °C display a solar power conversion efficiency of 5% when they are exposed to the solar light whose intensity is 71 mW/cm2. When the heterojunctions are directly polarized, they emit light in a broad band which is centered at ∼7700 A. An external electroluminescent emission efficiency of about 0.05% has been measured at liquid‐nitrogen temperature.
TL;DR: In this paper, the importance of the heter-junction interface and its dependence on material properties is discussed and various fabrication methods are discussed and their application to the different types of heter-structures.
Abstract: Heterojunctions have interesting optical properties which make them attractive for solar cells. Several types of heterostructure solar cells have been investigated: heteroface, abrupt heterojunction, and graded-gap heterojunction solar cells. The primary advantage of heterostructure cells is the enhanced short-wavelength response although there is potential for low-cost cells with polycrystalline material. The improvement in solar-cell performance for heterojunctions depends upon the selection of semiconductors with useful energy gaps that are closely matched in lattice-spacing and thermal-expansion coefficients. The importance of the heterojunction interface and its dependence on material properties is discussed. Various fabrication methods are discussed and their application to the different types of heterostructures. Recent performance data for material systems representative of each type of heterostructure cell are discussed and considered in terms of maximum expected performance.
Patent•
18 Nov 1977TL;DR: In this paper, the fabrication of periodic structures of (GaAs)n (AlAs)m, where m and n are the number of contiguous monolayers of GaAs and AlAs, respectively, in each period of the structure.
Abstract: Suitably modified molecular beam epitaxy (MBE) techniques are used to synthesize single crystal, periodic monolayer superlattices of semiconductor alloys on single crystal substrates maintained below a critical growth temperature. Described is the fabrication of periodic structures of (GaAs)n (AlAs)m, where m and n are the number of contiguous monolayers of GaAs and AlAs, respectively, in each period of the structure. As many as 10,000 monolayers were grown in a single structure. Also described is the MBE growth of (Alx Ga1-x As)n (Ge2)m, quasi-superlattice and non-superlattice structures depending on the particular values of n, m and the growth temperature. Waveguides, heterostructure lasers and X-ray reflectors using some of the structures are also described.
TL;DR: In this article, high performance backside illuminated photodiodes have been fabricated for the first time from InAs1−xSbx•InAs heterostructures prepared by liquid phase-epitaxy technique.
Abstract: High‐performance backside‐illuminated photodiodes have been fabricated for the first time from InAs1−xSbx‐InAs heterostructures prepared by liquid‐phase‐epitaxy technique. The peak wavelength can be tuned compositionally from 3.1 to over 7.0 μm at 77 K. The half‐width of the spectral responses as narrow as 1760 A (at 4.0 μm) have been achieved. Internal quantum efficiencies of 90% and zero‐bias‐resistance–area products of 2×107 Ω cm2 have been obtained at 77 K.
TL;DR: The photoelectronic properties of quaternary alloy heterojunction photodiodes made of liquid phase-grown In0.88Ga0.12As0.25P0.75 layers have been investigated experimentally and analytically as discussed by the authors.
Abstract: The photoelectronic properties of quaternary alloy heterojunction photodiodes made of liquid‐phase‐grown In0.88Ga0.12As0.25P0.75 layers deposited onto p‐doped InP substrates have been investigated experimentally and analytically. It is shown that a typical photodiode with a peak responsivity of 0.26 A/W (at 1.02 μm) has a quantum efficiency of ∼22% at 1.06 μm.
TL;DR: In this paper, the defect-current component was reduced in transistors grown at low temperature (∼750°C), and the variation of the electron diffusion length with the device operating temperature has been calculated by using the current gain at each temperature.
Abstract: n‐Ga1−xAlxAs/p‐GaAs/n‐GaAs heterojunction transistors with high Al concentrations have been fabricated by the conventional liquid‐phase epitaxial method. Electrical measurements showed that the transistors have a common emitter current gain of up to 1600. The current gain varies with the emitter injection level because of the defect‐current component, which is the recombination current in the depletion region. It has been made clear, however, that the effect of the defect current was reduced in transistors grown at low temperature (∼750 °C). The variation of the electron diffusion length Ln with the device operating temperature has been calculated by using the current gain at each temperature. Furthermore, the phototransistor characteristics have been widely investigated.
TL;DR: In this article, two new structures of lateral-injection transverse junction stripe (TJS) lasers, in which the stripe geometry is formed by the double heterojunctions, have been developed.
Abstract: Two new structures of lateral-injection transverse junction stripe (TJS) lasers, in which the stripe geometry is formed by the double heterojunctions, have been developed. These lasers, the homojunction type and the single-heterojunction type, have a self-reverse-biased p-n junction for concentrating current into the narrow active region. The temperature dependence of the threshold current has been very much improved in one of the new structures, the homojunction type, and is fair compared with those of good conventional broad-contact lasers. The threshold current does not increase rapidly up to 350 K in the homojunction lasers. These lasers exhibit improved characteristics of low threshold, the single longitudinal mode oscillation as well as the single fundamental transverse-mode oscillation, and "kink-free" behavior in the current depedence of the light-output power.
TL;DR: In this paper, the authors presented a cell with an open-circuit voltage of 0.63 V, a quantum efficiency of 1.82, a fill factor of 2.66, and a solar efficiency of 7.9 percent, in which the CdS is covered with an indium-tinoxide coating and then with an antireflection coating.
Abstract: n-CdS-p-CdTe heterojunctions have been prepared by close-spaced vapor transport of p-CdTe films onto single crystal n-CdS, by vacuum evaporation of n-CdS films onto single crystal p-CdTe, and by solution spraying of n-CdS films onto single crystal p-CdTe. In addition, a number of other II-VI p-n heterojunctions have been prepared by the close-spaced vapor transport technique. The highest solar efficiency to date has been obtained with a cell prepared by vacuum evaporation of n-CdS film onto p-CdTe crystal, in which the CdS is covered with an indium-tin-oxide coating and then with an antireflection coating; the photovoltaic parameters of this cell are an open-circuit voltage of 0.63 V, a quantum efficiency of 0.82, a fill factor of 0.66, and a solar efficiency of 7.9 percent. II-VI heterojunction cells with efficiency greater than 10 percent are expected in the near future.
Patent•
IBM1
TL;DR: In this paper, a semiconductor memory (storage) device is provided using layered semiconductor structures which produce spatially separate electron and hole wells, and the lifetime of the device depends upon whether or not charge carriers (electrons and holes) are confined in these wells.
Abstract: A semiconductor memory (storage) device is provided using layered semiconductor structures which produce spatially separate electron and hole wells. The state of the device depends upon whether or not charge carriers (electrons and holes) are confined in these wells. Thus, the device has a first state exhibiting one conductance or capacitance when the wells do not have charge carriers in them, and a second state (different conductance or capacitance) when charge carriers are confined in the potential wells. The lifetime of the state in which carriers are confined in the wells depends upon the amount of time required for electron-hole recombination and is expected to be very long since the electrons and holes are spatially separated. A preferred embodiment utilizes a layered heterostructure formed in the space charge region of a p-n junction. Electrons and holes are generated in the potential wells using either electrical injection or incident light, while reading is accomplished by measuring conductance or capacitance. Erasure of the device state is achieved by a reverse electrical bias which removes the electrons and holes from confinement in the potential wells. Confinement of electrons and holes in three dimensions is also achieved.
Patent•
06 Jan 1977TL;DR: In this article, an improved field-effect transistor is provided by forming the conducting channel boundary opposite the gate electrode as a heterojunction, where conduction electrons can penetrate the boundary very little and are constrained to the channel layer having good transport properties.
Abstract: An improved field-effect transistor is provided by forming the conducting channel boundary opposite the gate electrode as a heterojunction. For example a GaAs conducting channel may be bounded by an AlGaAs layer. The conduction electrons can penetrate the boundary very little and are constrained to the channel layer having good transport properties. The output conductance is reduced and the transconductance increased.
TL;DR: In this paper, the DLTS capacitance spectroscopy technique was used to search for interface states associated with an LPE GaAs/Al 0.22Ga0.78As heterojunction and the results can be interpreted in terms of well-known deep bulk states shifting abruptly at the interface with no observable interface states.
Abstract: We have used the DLTS capacitance spectroscopy technique to search for interface states associated with an LPE GaAs/Al0.22Ga0.78As heterojunction. The results can be interpreted in terms of well‐known deep bulk states shifting abruptly at the interface with no observable interface states. The limiting values are <5×108 and <4×109 cm−2 interface states (deeper than 0.1 eV) in the upper and lower half of the gap, respectively.
TL;DR: In this paper, multiple liquid phase epitaxy of In1−xGaxP1−z Asz•InP double heterojunctions, from a single set of Inrich melts, is demonstrated, and is shown to be a useful technique for the study of the problem of lattice matching at heterojunction interfaces and for growing large numbers of low-threshold (defect-free) DH laser wafers (λ∼1 μm).
Abstract: Multiple liquid phase epitaxy of In1−xGaxP1−z Asz‐InP double heterojunctions, from a single set of In‐rich melts, is demonstrated, and is shown to be a useful technique for the study of the problem of lattice matching at heterojunction interfaces and for growing large numbers of low‐threshold (’’defect‐free’’) DH laser wafers (λ∼1 μm).
Patent•
09 Mar 1977
TL;DR: In this paper, a stripe region and a contiguous region are made to have a difference in kinds and/or concentrations of impurity to give the stripe region a higher dielectric constant, preferably by about 0.01-1%, than the contiguous region.
Abstract: In an active layer restricted by a pair of heterojunctions in a semiconductor laser, a stripe region and a contiguous region are made to have a difference in kinds and/or concentrations of impurity to give the stripe region a higher dielectric constant, preferably by about 0.01-1%, than the contiguous region whereby transverse laser oscillation confined to the active layer by the heterojunctions is further confined to the stripe region in a width direction parallel to the heterojunctions. The dielectric constant profile established in the active layer stabilizes the transverse mode and eliminates nonlinearities in the laser output - exciting current curve as well as other undesirable performance characteristics that are exhibited in conventional stripe-geometry lasers. The difference in the impurity gives the stripe region a narrower band gap of from about 5 to about 100 meV than the contiguous region. For a laser of III-V-Group semiconductor materials, the difference is achieved by doping these regions with an n-type and/or a p-type impurity. The stripe width may be between about 1 micron and several tens of microns. The laser stably produces a single-mode optical output of 10 and 30 mW or more in CW and pulsed operation, respectively.
TL;DR: In this article, the first low-threshold red-light-emitting heterojunction laser diodes consisting of lattice-matched Ga(As,P)/(In,Ga)P heteroepitaxial layers were reported.
Abstract: The paper reports the first low-threshold red-light-emitting heterojunction laser diodes consisting of lattice-matched Ga(As,P)/(In,Ga)P heteroepitaxial layers. A room-temperature threshold current of 3400 A/sq cm was obtained at a wavelength of about 7000 A; this value is substantially lower than those achieved at this wavelength with (Al,Ga)As lasers. For the first time, continuous-wave laser operation at temperatures as high as 10 C has been obtained for GaAs(1-x)P(x).
TL;DR: In this article, a CdS/InP heterojunction solar cells are fabricated by evaporating indium-doped Cd-S films on zinc-Doped InP surfaces, achieving a collection efficiency of 70% at a wavelength of 0.65 µm.
Abstract: Heterojunctions on polycrystalline indium phosphide films are fatbricated and characterized. The InP films are chemically deposited on molybdenum substrates. Cuprous selenide films, being cubic in crystal structure and degenerate in conduction, are prepared on n-type InP films. CuxSe/InP thin film solar cells have efficiencies of up to 1.7% with a short circuit current density of 11 mA/cm2 under AM 1 simulated irradiation. Furthermore, CdS/InP heterojunction solar cells are fabricated by evaporating indium-doped CdS films on zinc-doped InP surfaces. The efficiency directly increases with the annealing temperature of the cells up to 2.0% with a short-circuit current density of 18 mA/cm2. A collection efficiency of 70% is obtained at a wavelength of 0.65 µm from a spectral response curve. In addition, the electron diffusion length is calculated to be 0.2 µm, which determines the lower collection efficiency at longer wavelengths.
TL;DR: In this article, the authors have fabricated heterojunction photovoltaic devices consisting of RF-sputtered, highly transparent, and conductive indium-tinoxide (IT0) films deposited onto both amorphous or crystalline Si.
Abstract: We have fabricated heterojunction photovoltaic devices consisting of RF-sputtered, highly transparent, and conductive indium-tin-oxide (IT0) films deposited onto both amorphous or crystalline Si. The ITO-amorphous-Si devices exhibit photovoltaic energy-conversion efficiencies of the order of 0.01 percent for the 100-mW/cm2 white light of a tungsten-halogen lamp. However, the relatively high photoresponse of these devices in the blue-UV spectral region leads to a photovoltaic conversion efficiency of approximately 0.5 percent for monochromatic light of wavelength 400 nm. The ITO-crystalline-Si devices exhibit terrestrial solar-cell efficiencies of the order of 1 percent. The performance of such a cell strongly depends on the insulating interface oxide layer, on the surface-state density, and on the incident-light intensity. A model for the operation of these devices is presented and shown to be in quantitative agreement with the experimental data.