Showing papers on "Heterojunction published in 1974"

Quantum States of Confined Carriers in Very Thin Al x Ga 1 − x As -GaAs- Al x Ga 1 − x As Heterostructures

Abstract: Quantum levels associated with the confinement of carriers in very thin, molecular-beam—grown AlxGa1−xAs−GaAs-Alx Ga1−xAs heterostructures result in pronounced structure in the GaAs optical absorption spectrum Up to eight resolved exciton transitions, associated with different bound-electron and bound-hole states, have been observed The heterostructure behaves as a simple rectangular potential well with a depth of ≈088ΔE g , for confining electrons and ≈012ΔE g for confining holes, where ΔE g is the difference in the semiconductor energy gaps

CuInSe2/CdS heterojunction photovoltaic detectors

Abstract: We report CuInSe2/CdS p‐n heterojunction photovoltaic detectors which display uniform quantum efficiencies of up to ∼70% between 0.55 and 1.25 μ. Response times as short as 5 nsec have been observed. A weak electroluminescence (0.01% external quantum efficiency) peaking near 1.4 μ has also been observed at room temperature.

Distributed‐feedback single heterojunction GaAs diode laser

Abstract: Laser operation utilizing distributed feedback (DFB) in single heterojunction (SH) GaAs/GaAlAs diodes is reported. Laser wavelengths ranging from 8430 to 8560 A were observed in various samples depending on grating period. The threshold current densities required were comparable to those of normal SH diodes.

Optical absorption and photoluminescence studies of thin GaAs layers in GaAs–AlxGa1−xAs double heterostructures

Abstract: A three‐layered AlxGa1−xAs–GaAs–Alx Ga1−xAs structure has been used to measure the optical absorption and photoluminescence in thin GaAs layers prepared by liquid‐phase epitaxy. The results presented here are for lightly doped n‐type GaAs with free‐carrier concentrations near 1016 cm−3; however, the technique can be used for arbitrarily doped material. The absorption coefficient α was measured between 1.4 and 2.2 eV at 2 and 298 K. The absorption strength at the band gap was found to be (1.15×104)±1000 cm−1 at 2 K and (0.99×104)±1000 cm−1 at 298 K. At 1.96 eV, the energy of the He–Ne laser commonly used for photoexcitation of GaAs, α at 298 K was measured to be 4.4×104 cm−1. A value of 3.8 meV for the room‐temperature exciton binding energy was inferred from the temperature dependence of the interband absorption strength. This value together with previous reflectivity data for high‐purity GaAs gives the energy gap of pure unstrained GaAs at 298 K as 1.424±0.001 eV. The effects of strain due to lattice mis...

GaAs–AlxGa1−xAs heterostructure laser with separate optical and carrier confinement

Abstract: Heterostructure injection lasers in which the GaAs active region is the center layer of a five‐layer dielectric slab waveguide have been investigated. The GaAs active layer is bounded on each side by an AlxGa1−xAs layer to confine the carriers. The two outside layers which are AlyGa1−yAs(y > x) confine the optical field. Lasers with this structure have been fabricated and room‐temperature threshold current densities Jth300 as low as 650 A/cm2 have been obtained for 1‐mm cavity lengths. Differential quantum efficiencies ηD for these separate optical and carrier confinement heterostructure (SCH) lasers were higher than generally encountered for double‐heterostructure (DH) lasers with values as high as 65% for [inverted lazy s]300−μ−long cavities. The external quantum efficiency of several typical units was determined as a function of input current, and for one representative unit a maximum value of 39% was obtained at about four times Jth300. Emission in the fundamental TE mode was obtained for symmetrical ...

Heat treatment effects in Cu2S-CdS heterojunction photovoltaic cells

Abstract: The optical and electronic properties of single crystal Cu2S-CdS photovoltaic cells were investigated. In these cells trapped charge near the interface which is manifested by a persistent increase in junction capacitance (the photocapacitance) plays a significant role in determining the carrier transport properties. It was found that the severe degradation in short-circuit current observed in heat-treated cells can be separated into two components: (1) a relatively small thermal component occurring on heat-treatment in the dark, and (2) a much larger degradation caused by exposure to light at room temperature. By a short additional heat-treatment above approximately 100 C the cell can be completely restored to its condition before the optically caused degradation with no effect on the depletion layer width.

Liquid phase epitaxial growth of laser heterostructures in Pb1−xSnxTe

Abstract: Pb1−xSnxTe heterostructures have been grown by liquid phase epitaxy on p‐PbTe substrates and laser diodes have been fabricated from layered structures with the following compositions: n‐PbTe (LPE)/p‐PbTe (substrate); n‐Pb1−xSnxTe (LPE)/p‐PbTe (substrate); and n‐PbTe (LPE)/n‐Pb1−xSnxTe (LPE)/p‐PbTe (substrate). Lasing in all structures occurs in the lower‐band‐gap region. Threshold currents in these lasers are comparable to those reported for conventional diffused lasers, indicating that the presence of the heterojunctions does not introduce a significant number of new nonradiative recombination centers and that efficient minority carrier injection occurs across the heterojunctions. The liquid phase epitaxy technique used in these growths is discussed.

Double‐heterostructure GaAs distributed‐feedback laser

Abstract: The fabrication and operation of a GaAs–GaAlAs heterostructure distributed‐feedback laser are described in which fine optical corrugations (≈ 1150 A) are etched and regrown into the interface between two layers of the heterostructure. Laser operation has been observed before and after the growth of the final layer with optical pumping.

Degradation of AlxGa1−xAs heterojunction electroluminescent devices

Abstract: Experimental results are presented correlating the operating life of (AlGa)As heterojunction diodes with recombination region doping and Al concentration. For a given doping level, the operating life is shown to increase with the addition of Al. The relationship between spontaneous emission degradation and lasing properties has also been studied.

Threshold reduction in Pb1−xSnx Te laser diodes through the use of double heterojunction geometries

Abstract: A systematic study has been made of the effect of the middle active region width in double heterojunction Pb1−xSnx Te/PbTe laser diodes on the lasing threshold. A fourfold reduction in pulsed threshold over that of comparable single heterojunction lasers is demonstrated in lasers having 4‐μm‐wide middle regions. A comparison is also made between lasers fabricated by liquid phase epitaxy using undoped melts and substrates, and using thallium‐doped p ‐type PbTe layers; the latter is shown to yield thresholds as much as two times lower.

Properties of Ge-doped GaAs and Al x Ga 1-x As, Sn-doped Al x Ga 1-x As and Si-Te-doped GaAs

Abstract: In order to better understand the electrical and optical properties of GaAs and AlxGa1-x As used in making double heterojunction lasers, we have studied the Hall coefficient, resistivity and photoluminescence behavior of doped epitaxial samples of these materials. In particular, we report results on Ge-doped GaAs and Alx Ga1-x As, Sn-doped AlxGa1-x As and Si-Te-doped GaAs single crystal layers which were grown on GaAs substrates by the liquid phase epitaxial method. The effects of impurities in the solution on the carrier concentration, mobility, photoluminescence spectra and possible recombination processes in these layers are discussed.

Method of making a double heterojunction diode laser

Abstract: A method for improving the current confinement capacity of a double heterojunction laser by using a high energy implantation of oxygen in the regions of an injection laser surrounding the active region of such laser so as to make such regions semi-insulating.

Heterojunction photovoltaic devices employing i-iii-vi compounds

Abstract: Photovoltaic devices are constructed from a principal body of copper indium selenide (CuInSe 2 ) upon which is deposited a hetero-epitaxial layer of a high bandgap semiconductor, such as an n-type layer of cadmium sulfide (CdS). When made with a high-resistance intermediate region, the device is a photovoltaic detector for modulated radiation and has a response time as low as 5 nsec for a reverse bias of approximately two to three volts. When made without a high-resistance intermediate region (e.g., an abrupt p-n heterojunction) the device is a useful solar cell. In these forms of the device, absolute photovoltaic quantum efficiencies up to 70 percent have been observed. The quantum efficiency of the solar cell type of device is reasonably flat between 0.55 and 1.25 μm. With forward bias, the device is a light-emitting diode with external electro-luminescent quantum efficiency of ˜1×10 - 4 at room temperature and ˜1×10 - 2 at 77°K, liquid nitrogen temperature.

Liquid phase epitaxial (LPE) grown junction In1-xGaxP (x∼0.63) laser of wavelength λ∼5900 Å (2.10 eV, 77°K)

Abstract: Laser operation (77 °K) of In1−xGaxP LPE p‐n junctions is demonstrated at λ∼5900 A (2.10 eV, yellow). The junctions are prepared by the sequential growth (on GaAs1−yPy substrates) of first an n‐type layer and then a Zn‐doped p‐type layer (not compensated). During growth of the p‐type layer, Zn diffuses slightly (at reduced concentration) into the first layer, yielding a thin compensated active layer. The structure which results approximates in operation the behavior of a single heterojunction. Although the threshold for the laser operation of these devices is fairly high, it is demonstrated, nevertheless, that In1−xGaxP LPE grown junctions can be operated as lasers and, furthermore, at wavelengths λ ≲ 5900A.

Room‐temperature heterojunction laser diodes from vapor‐grown In1−xGaxP/GaAs structures

Abstract: Vapor‐grown epitaxial structures of In0.5Ga0.5P/GaAs have yielded heterojunction laser diodes with room‐temperature threshold current densities as low as 8000 A/cm2 for a 2.5‐μm GaAs laser cavity width. Differential external quantum efficiencies as high as 30% have been attained. Measurements suggest the existence of internally ``trapped'' laser modes due to the large refractive‐index discontinuity at the In0.5Ga0.5P–GaAs interfaces.

On‐state characteristics of amorphous/crystalline heterojunctions

Abstract: Band models previously applied to off‐state chalcogenide‐glass/crystalline Si heterojunctions are shown to be applicable to these devices after the threshold‐type glass is switched into the on state. In addition, it appears that the on state can be maintained by the injection of electrons from the amorphous semiconductor into n‐type Si, contrary to some double‐injection models for threshold switching.

Effects of doping and free carriers on the refractive index of direct-gap semiconductors

Abstract: A model for the doping and current dependence of the refractive index of direct-gap semiconductors has been developed and applied to GaAs in order to explain certain properties of single heterostructure injection lasers. The model involves the concept of an effective energy gap which takes account of the effects of doping and free carriers via the Burstein shift, the exchange interaction, and the average screened Coulomb potential of the impurities. This effective gap, together with empirical results for the energy dependence of the refractive index, facilitates the calculation of refractive index changes with doping and current. Numerical results are given for GaAs, and the model is applied particularly to the substrate and active regions of single heterostructure injection lasers. In these devices the refractive index values are particularly important in determining the dielectric waveguide properties. With the aid of our model, this feature can be discussed in detail, with special reference to the breakdown of the waveguide effect which occurs (a) for substrate doping levels below a critical value, and (b) for currents well above threshold ('saturation').

MBE growth: gettering contaminants and fabricating heterostructure junction lasers

Abstract: In the fabrication of double heterostructure GaAsAlGaAs junction lasers by molecular beam epitaxy, it has been found that suitably annealing the entire heterostructure increases the external quantum efficiency of the laser and reduces the room temperature threshold for lasing. Also described is a technique using relatively uncollimated beams to deposit continuously on the interior walls of the vacuum chamber fresh layers which getter deleterious contaminants. In addition, pyrolytic boron nitride, rather than graphite, effusion cells are utilized in order to reduce the amount of CO formation in the system.

Properties of Schottky barriers and p‐n junctions prepared with GaAs and Alx Ga1−x As molecular beam epitaxial layers

Abstract: The properties of molecular beam epitaxy (MBE) that are relevant to device applications have been investigated. Precise control of layer thickness is one of the most attractive features of MBE, and layers from a few hundred angstroms to 10 μ may readily be grown. Unintentionally doped GaAs layers grown on 〈100〉‐oriented substrates are n type, and room‐temperature carrier concentrations of ∼2 × 1015 cm−3 with a mobility of ∼6000 cm2/V sec have been obtained. Schottky barriers on MBE n‐type GaAs layers demonstrate that defect‐free devices with uniform properties may be prepared at the present time. Junctions of p‐ and n‐type MBE have also been fabricated and have been found to compare favorably with p‐n junctions prepared by other techniques. Heterojunctions of GaAs and Alx Ga1−xAs have also been prepared and evaluated. The p‐type Alx Ga1−xAs layers are suitable for heterostructure applications, while n‐type Alx Ga1−xAs layers tend to be high resistivity at the present time.

Light‐emitting mechanism of ZnTe–CdS heterojunction diodes

Abstract: ZnTe–CdS heterojunction LED, which was prepared on the ZnTe substrate by CdS vapor growth, showed the red light emission at 300°K. The EL spectra had a peak at 1.78–1.80 eV at 300°K, and two peaks at about 2.10 and 1.55 eV at 77°K. The existence of the ZnxCd1−xTe mixed crystal with a graded band structure at the heterojunction interface was shown from the results of the photovoltage spectra and transmittance analysis of the heterojunction. The formation of the mixed crystal was found to be due to Cd diffusion into the ZnTe substrate during the epitaxial growth. From photoluminescence measurements, it is concluded that the red emission of ZnTe–CdS LED may originate from the ZnxCd1−xTe mixed crystal layer. Thus, efficient red emission could be obtained in our ZnTe–CdS heterojunctions on account of the mixed crystal layer, which reduced high‐energy barriers for electrons and holes.

Calculation of the minority‐carrier confinement properties of III‐V semiconductor heterojunctions (applied to transmission‐mode photocathodes)

Abstract: For electro‐optical device applications, the principal properties desired of a heterojunctions are minority‐carrier confinement and a change in optical parameters. It is shown that for III‐V materials with heavily doped junctions the minority‐carrier confinement properties may be approximately calculated from the materials parameters by using a simple relationship. The critical parameters are shown to be the minority‐carrier diffusion length, the device operating temperature, and the rate at which the band gap of a materials system varies with lattice constant. The effective interfacial recombination velocity into the high‐band‐gap side of a heterojunction is calculated from these parameters, and is in turn used to calculate the properties of transmission‐mode III‐V photocathode devices. Some materials systems such as GaAs–AlGaAs and InP–InGaAsP demonstrate near‐ideal performance as photocathodes, while other commonly used materials systems such as GaAs–GaAsP are shown to be fundamentally incapable of goo...

Luminescent properties of CuGaS2 doped with Cd or Zn

Abstract: The photoluminescence spectra of CuGaS2 crystals doped with Cd or Zn vary continuously from a green emission (0.51 μ) to an orange emission (∼ 0.59 μ) depending upon the concentrations of Cd and Zn. The room‐temperature internal quantum efficiency is reproducibly 0.2%. The electroluminescent efficiencies of CuGaS2: CdS heterojunction LEDs fabricated by using these substrates are not appreciably higher than the best efficiencies reported earlier.

Formation of interface states and defects in GaAs–AlxGa1−xAs DH lasers under room‐temperature cw operation

Abstract: Experimental results of an investigation on the nature of degradation‐induced defects in AlxGa1−xAs–GaAs double‐heterostructure injection lasers are presented. The variation of junction capacitance data before and after aging indicates that defects are generated initially at the p‐n heterojunction interface and later spread into the active layer as traps. The density of interface states is calculated to be on the order of 1012 cm−2 and the density of traps in the active layer is calculated to be greater than 1017 cm−3. In addition, the carrier lifetime is measured by using both the delay‐time and voltage‐decay methods. After degradation, the carrier lifetime reduces slightly at the appearance of interface states but shows significant changes when traps are detected in the active layer. An explanation is given and correlated with the threshold‐current variation.

Preparation and properties of CdSnP2/InP heterojunctions grown by LPE from Sn solution

Abstract: Heterojunctions of n‐type CdSnP2 on p‐type InP substrates have been prepared by LPE from Sn solutions. The tipping arrangement, solution composition, and temperature program for the preparation of high‐quality LPE layers are described. Heterodiodes prepared from such LPE wafers electroluminesce under forward bias at wavelengths near 1.6 μ with internal quantum efficiencies approaching 2% at room temperature. When used as photovoltaic detectors, the quantum efficiency of these diodes surpasses that of Si for λ>1.09 μ and exceeds 1% for all wavelengths between 0.96 and 1.3 μ.

Amorphous‐Crystalline Heterojunctions

Abstract: Junctions between amorphous and crystalline semiconductors are investigated theoretically. A new type of junction is formed if the dominant conduction mechanism in the amorphous semiconductor is hopping near the Fermi level. In this case the junctions are expected to exhibit qualitatively different behavior than conventional semiconductor‐ semiconductor or semiconductor‐metal junctions. Current and capacitance as a function of applied voltage are calculated for a simple model. We point out how these measurements can give information about the position of the Fermi‐level and the density of states in the amorphous material.

The preparation of CdSnP2/InP heterojunctions by liquid phase epitaxy from Sn-solution

Abstract: Heterojunctions of n-type CdSnP2 on p-type InP substrates are prepared by LPE from Sn-solutions. The significance of the tipping arrangement, of the initial solution composition and of the temperature program for preparing LPE layers of high quality is discussed. Heterodiodes cleaved from such LPE wafers electroluminesce under forward bias between 1 µm and 1.8 %m with internal quantum efficiencies approaching 1.8% at room temperature. When used as photovoltaic detectors, the quantum efficiency of these diodes surpasses that of Si for λ > 1.09 µ, and exceeds 1% for all wave-lengths between 0.96 and 1.3 µ.