Showing papers on "Heterojunction published in 1985"
TL;DR: In this article, a negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region is proposed.
Abstract: We propose a new negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region. The key difference compared to previously studied structures is that resonant tunneling is achieved by high‐energy minority carrier injection into the quantum state rather than by application of an electric field. Thus this novel geometry maintains the crucial, structural symmetry of the double barrier, allowing unity transmission at all resonance peaks and higher peak‐to‐valley ratios and currents compared to conventional resonant tunneling structures. Both tunneling and ballistic injection in the base are considered. These new functional devices have significant potential for a variety of signal processing and multiple‐valued logic applications and for the study of the physics of transport in superlattices.
314 citations
284 citations
TL;DR: In this article, the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy was measured using photocurrent spectroscopy.
Abstract: We have used photocurrent spectroscopy to measure the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy A dramatic lowering of the indirect band gap, relative to that of unstrained bulk Ge‐Si alloys, is observed Our results for 0≤x≤07 are in remarkably good agreement with recent calculations of the effects of misfit strain on the band edges of coherently strained Ge‐Si heterostructures At x=06, the gap is lower than that of pure Ge
281 citations
TL;DR: The first direct determination of carrier-energy-loss rates in a semiconductor is reported, providing fundamental insight into carrier-phonon interactions in semiconductors.
Abstract: We report the first direct determination of carrier-energy-loss rates in a semiconductor. These measurements provide fundamental insight into carrier-phonon interactions in semiconductors. Unexpectedly large differences are found in the energy-loss rates for electrons and holes in GaAs/AlGaAs quantum wells. This large difference results from an anomalously low electron-energy-loss rate, which we attribute to the presence of nonequilibrium optical phonons rather than the effects of reduced dimensionality or dynamic screening.
269 citations
TL;DR: In this article, the crystal orientation dependence of n− and p−type Si doping in molecular beam epitaxial GaAs was investigated and high electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes were demonstrated for the first time.
Abstract: Results on crystal orientation dependence of n‐ and p‐type Si doping in molecular beam epitaxial GaAs are presented. High electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes are demonstrated for the first time. The doping results should prove useful for various transistor structures and complementary circuits. Also, due to the differences in the band structure for different orientations, quantum well heterostructures are likely to exhibit many interesting phenomena which are strongly orientation dependent.
207 citations
TL;DR: In this article, the optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature.
Abstract: The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation‐doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction‐band offset of 60% of the band‐gap discontinuity. For modulation‐doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two‐dimensional electron gas.
185 citations
TL;DR: The measured scattering-time ratio is a new method of directly selecting the dominant scattering mechanism among competing effects, and is in excellent agreement with the calculated screened-Coulomb scattering from residual charge centers in the AlGaAs, while the lack of this effect in the MOSFET's is incellent agreementwith the surface roughness calculation.
Abstract: Recent theoretical and experimental interest has focused on the issue of the dominant scattering mechanism which limits the mobility of the two-dimensional electron gas formed at the molecular-beam-epitaxy (MBE) interface of an AlGaAs/GaAs heterojunction. Measurements have been made at 1.3 K with MBE-grown AlGaAs/GaAs heterojunctions, indicating a difference of nearly an order of magnitude between transport scattering times, expressed as a mobility, measured via either the Hall mobility (classical scattering time) or from the de Haas--Shubnikov oscillation envelope (quantum scattering time). This result is contrasted with measurements from the qualitatively different Si metal-oxide-semiconductor field-effect transistor (MOSFET) interface where, over the same charge-density region, the two mobilities are nearly equal and limited by interface roughness scattering. The ratio of the quantum-to-classical scattering time from competing scattering mechanisms is calculated. The observed low ratio in the heterostructures is in excellent agreement with the calculated screened-Coulomb scattering from residual charge centers in the AlGaAs, while the lack of this effect in the MOSFET's is in excellent agreement with the surface roughness calculation. The measured scattering-time ratio is thus a new method of directly selecting the dominant scattering mechanism among competing effects. Stray effects which could interfere with the quantum measurements are discussed.
164 citations
TL;DR: In this paper, the breakdown of the Quantum Hall effect observed on GaAs-AlGaAs samples is quantitatively explained in terms of peculiar electron-heating characteristic to the quantum Hall regime.
156 citations
TL;DR: In this paper, the authors observed resonant tunneling of holes through double-barrier AlAs•GaAs•AlAs structures sandwiched between p+−GaAs regions, where the resonances appeared as negative resistance regions in the currentvoltage characteristics perpendicular to the interface planes.
Abstract: We have observed resonant tunneling of holes through double‐barrier AlAs‐GaAs‐AlAs structures sandwiched between p+‐GaAs regions. The resonances appeared as negative resistance regions in the current‐voltage characteristics perpendicular to the interface planes. A set of resonant structures was already visible at high temperatures (T≂250 K) while an additional set was observable only at low temperatures (T≤100 K). Although in principle the sets can be attributed to tunneling of light and heavy holes, respectively, an analysis of the number and relative voltage position of the resonances suggests that considerable band mixing occurs. The application of a strong magnetic field, parallel to the tunneling current, introduced shifts in the resonances which support that interpretation.
145 citations
01 Jun 1985
TL;DR: The basic concepts and first-order growth model derived from the RHEED intensity oscillation technique are described and the limitations imposed by the experimentally demonstrated multiple-scattering nature of the diffraction process are indicated.
145 citations
TL;DR: In this article, a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces is presented, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides.
Abstract: We present a theoretical study of the structural and electronic properties of pseudomorphic Si/Ge interfaces, in which the layers are strained such that the lattice spacing parallel to the interface is equal on both sides. The self‐consistent calculations, based on the local density functional and ab initio pseudopotentials, determine the minimum energy configurations, and the relative position of the Si and Ge bands. The presence of the strains influences the interface dipole, and also causes significant shifts and splittings of the bulk bands. For (001) interfaces we find for the top of the valence bands: Ev, Ge−Ev, Si=0.74 and 0.21 eV, respectively, for the cases corresponding to Ge strained to match a Si substrate and vice versa. A discussion of these results and comparison with experiment is presented.
IBM1
TL;DR: Luminescence data reveal large electronic energy shifts relative to bulk energy levels which can be used to calculate the confinement energy of the localized electrons in a simple borosilicate glass system.
Abstract: Finite size effects have been observed at low temperatures for electrons confined to semiconductor microcrystallites embedded in a simple borosilicate glass. Luminescence data reveal large electronic energy shifts relative to bulk energy levels which can be used to calculate the confinement energy of the localized electrons. This system provides an attractive alternative to quantum well heterostructures, permitting direct optical studies of electron-confinement effects over a wide range of temperatures.
TL;DR: The first observation of strong and well-resolved exciton peaks in the room-temperature absorption spectra of infrared band-gap multiple quantum well structures (MQW) was reported in this article.
Abstract: The first observation of strong and well‐resolved exciton peaks in the room‐temperature absorption spectra of infrared band‐gap multiple quantum well structures (MQW’s) is reported. Assignment of the optical resonances in the absorption spectra of GaInAs/AlInAs MQW’s yields the material parameters of this new heterojunction. The discontinuities of the conduction and valence bands are found to be ΔEc=0.44 eV and ΔEv=0.29 eV, respectively.
TL;DR: In this paper, the molecular beam epitaxial growth of GaAs on Si(211) has been investigated and the experimental results support the theoretical prediction, and the (211) layer growth is initiated with a thin (GaAs/Al, GaAs) superlattice buffer (0.1 μm), consisting of 10 periods of 5+5 nm.
Abstract: The molecular beam epitaxial growth of GaAs on Si(211) has been investigated. Theoretical considerations had suggested the (211) orientation to be particularly suitable for the nucleation and growth of a zincblende‐type compound semiconductor on a diamond‐type elemental one. The experimental results support the theoretical prediction. Morphologies of thin (≤0.1 μm) (211) layers are substantially better than for (100) layers, which nucleate poorly and require large layer thicknesses (≂1μm) to yield good morphologies. When the (211) layer growth is initiated with a thin (GaAs/Al, Ga)As superlattice buffer (0.1 μm), consisting of 10 periods of 5+5 nm, the (211) morphology rivals that of GaAs(100) homoepitaxial growth. Chemical etching studies as well as transmission electron microscope investigations show the layers to have the (211)B orientation and to be free of antiphase domains, both as predicted. The (211) layers show strong photoluminescence at 4 K. Not intentionally doped layers are n type, with elect...
TL;DR: In this article, a novel emitter edge-thinning structure was adopted for Npn Al 0.5Ga0.5As/GaAs single heterojunction bipolar transistors grown by liquid phase epitaxy.
Abstract: A novel emitter edge‐thinning structure was adopted for Npn Al0.5Ga0.5As/GaAs single heterojunction bipolar transistors grown by liquid phase epitaxy. In this structure, the emitter edge was etched down to approximately 0.1 μm thick such that the surface and emitter‐base junction depletion regions could touch each other. As a result, the current is blocked from the emitter periphery and the surface leakage current is reduced which improves the current gain especially at low operating current. The best device thus obtained shows a common emitter current gain of 12 500 at a collector current of 50 mA which is the highest gain reported to date for the heterojunction bipolar transistors. The current gain characteristics were indeed improved especially at a collector current below 10 μA.
TL;DR: In this article, the effect of band bending in undoped AlxGa1−xAs due to negative charge on measured barrier heights and on C-V curves was analyzed in terms of thermionic emission to derive barrier heights at the n+ GaAs-Al0.4Ga0.6As interface φG.
Abstract: We have combined current‐voltage (I‐V) and capacitance‐voltage (C‐V) measurements on n− GaAs–Al0.4Ga0.6As–n+ GaAs capacitors with different thicknesses of Al0.4Ga0.6As to determine the conduction‐band discontinuity at the Al0.4Ga0.6As–n+ GaAs interface. Undoped AlxGa1−xAs deposited by molecular‐beam epitaxy contains negative charge. We calculate the effect of band bending in undoped AlxGa1−xAs due to negative charge on measured barrier heights and on C‐V curves. The temperature dependence of I‐V curves is analyzed in terms of thermionic emission to derive barrier heights at the n+ GaAs–Al0.4Ga0.6As interface φG. Measured values of φG are proportional to the square of the insulator thickness, w, showing that negative charge is uniformly distributed through undoped Al0.4Ga0.6As. Combining values of Fermi energy and band bending at zero bias with φG at zero Al0.4Ga0.6As thickness, we find that the value of the barrier discontinuity for n+ GaAs–Al0.4Ga0.6As is ∼0.30 V. This corresponds to a ratio of conduction‐band discontinuity ΔEC to band‐gap difference ΔEG of 0.63±0.03, which is appreciably less than the value 0.85±0.03 that is widely accepted. We find that the dielectric constant of Al0.4Ga0.6As is more temperature dependent than that of GaAs between 77 and 250 K.
TL;DR: In this paper, the effects of the electron-LO-phonon interaction effects on the electronic properties of a single two-dimensional electron layer (as occurring, for example, in artificially structured single quantum wells or heterojunctions made of III-V or II-VI semiconducting materials) are discussed theoretically.
TL;DR: In this paper, the conduction band-discontinuity ΔEc and the valence-band discontinuity ΔEv were independently obtained by the C-V profiling technique, taking into account a correction for the interface charge density.
Abstract: The band discontinuity has been determined for a GaAs/AlGaAs heterojunction prepared by molecular beam epitaxy. The conduction band‐discontinuity ΔEc and the valence‐band discontinuity ΔEv were independently obtained by the C‐V profiling technique, taking into account a correction for the interface charge density. The simulation was employed to confirm the reliability of the obtained band discontinuity. The ΔEc dependence on both the Al composition of the AlGaAs layer and the heterojunction structure (AlGaAs on GaAs, or GaAs on AlGaAs) was examined. We found that ΔEc and ΔEv were determined to be 62 and 38% of the band‐gap discontinuity ΔEg, being independent of the structure.
TL;DR: In this article, the authors studied the electrical properties of a GaAs/AlxGa1-xAs modulation doped heterostructure where there are parallel competing conduction paths in the 2D gas at the interface and in the undepleted AlxGa 1 -xAs.
Abstract: Presents the results of a study of the electrical properties of a GaAs/AlxGa1-xAs modulation doped heterostructure where there are parallel competing conduction paths in the 2D gas at the GaAs/AlxGa1-xAs interface and in the undepleted AlxGa1-xAs. The authors show that the presence of these two paths introduces a magnetic field dependence into the measured resistivity and Hall coefficient of the heterostructure. This magnetic field dependence is analysed in order to determine the carrier densities and mobilities in the separate layers. This analysis is then used to investigate the effects of illumination on the heterojunction and to explain partially the temperature dependence of the properties of the heterojunction.
TL;DR: In this paper, the subband structure of a two-dimensional hole system at GaAs/AlGaAs heterojunctions and quantum wells is calculated in the selfconsistent Hartree approximation.
Abstract: The subband structure of a two-dimensional hole system at GaAs/AlGaAs heterojunctions and quantum wells is calculated in the self-consistent Hartree approximation. The subband dispersion is shown to be quite nonparabolic and anisotropic. The cyclotron effective mass is strongly dependent on the hole concentration. The spin splitting is extremely large due to the lack of inversion symmetry at single heterojunctions. Light-scattering spectra are calculated for quantum wells and the agreement with experiments is excellent for systems with low hole concentrations.
TL;DR: In this paper, the application of x-ray photoemission spectroscopy (XPS) to the direct, contactless, and quantitative measurement of the valence band discontinuity (ΔEv) at abrupt heterojunctions is discussed.
Abstract: Accurate knowledge of the band discontinuities at a heterojunction interface and the factors that affect their magnitude are of both fundamental and practical interest. The application of x‐ray photoemission spectroscopy (XPS) to the direct, contactless, and quantitative measurement of the valence band discontinuity (ΔEv) at abrupt heterojunctions is discussed. The topics covered include a description of a method to achieve precise measurement, results of ΔEv measurements for many heterojunction pairs selected from the lattice‐matched semiconductor series Ge, GaAs, ZnSe, CuBr, and AlAs, and a comparison of experiment to models that predict ΔEv. Examples are given to illustrate the effect on ΔEv of such preparation‐dependent parameters as growth sequence and interface crystallographic orientation.
TL;DR: Stained-layer epitaxy overcomes problems of crystallographic compatibility and produces high-quality heterostructures of germanium-silicon layers on silicon, which opens the door to a range of electronic and photonic devices that are based on bandstructure physics.
Abstract: Despite the dominant position of silicon in semiconductor electronics, its use is ultimately limited by its incompatibility with other semiconducting materials. Strained-layer epitaxy overcomes problems of crystallographic compatibility and produces high-quality heterostructures of germanium-silicon layers on silicon. This opens the door to a range of electronic and photonic devices that are based on bandstructure physics.
TL;DR: In this paper, the conduction and valence-band barrier heights at an abrupt intrinsic semiconductor-semiconductor heterojunction via a doping interface dipole were artificially tuned by means of ultrathin ionized donor and acceptor sheets in situ grown within ≲100 A from the heterointerface.
Abstract: We have succeeded for the first time in artificially tuning the conduction and valence‐band barrier heights at an abrupt intrinsic semiconductor‐semiconductor heterojunction via a doping interface dipole (DID). This is achieved by means of ultrathin ionized donor and acceptor sheets in situ grown within ≲100 A from the heterointerface by molecular beam epitaxy. In the limit of a few atomic layers separation between the charge sheets this amounts to modify the effective band‐edge discontinuities. A near one order of magnitude enhancement in the photocollection efficiency of an abrupt AlGaAs/GaAs heterojunction has been observed as result of the conduction‐band barrier lowering induced by the DID.
TL;DR: In this article, a polycrystalline thin-film solar cell utilizing a backwall designed heterojunction structure based upon p-type Cu2−xSe and n-type CdS semiconductor materials is described.
Abstract: The development of a polycrystalline thin‐film solar cell utilizing a backwall designed heterojunction structure based upon p‐type Cu2−xSe and n‐type CdS semiconductor materials is described. The electrical, optical, and structural properties of the deposited thin‐film materials are described. A device efficiency of 5.38% under simulated AM1 illumination is reported.
TL;DR: The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented in this article, where the flux composition as a function of epitaxial layer composition was determined for the lattice matching quaternary.
Abstract: The growth of useful GaxIn1−xPyAs1−y by MBE is inhibited by the difficulty in maintaining precise control over the flux from condensed source As and P effusion ovens. The use of P2 and As2 beams generated from the cracking of PH3 and AsH3 as an alternative approach is reviewed and new data are presented. Accommodation coefficients were determined for P2 and As2 on heated InP and GaAs surfaces. The flux composition as a function of epitaxial layer composition was determined for the lattice‐matching quaternary. Studies of doping were done and injection laser structures were grown. Although detailed studies of layer composition control were not done, the achievable control seems quite adequate for injection lasers. A variety of heterostructure lasers emitting at nominally 1.5 μm with broad area 300‐K threshold‐current densities from 1300 to 2400 A/cm2 were demonstrated. Ridge waveguide lasers fabricated from the same wafers had Ith of about 40 mA and differential efficiencies of 36%–45%. They lased cw to 50 °C.
TL;DR: The first N-p-n heterojunction bipolar transistor (HBT) using a (Ga,In)P/GaAs heter-junction emitter on a GaAs base was reported in this article.
Abstract: We report the first N-p-n heterojunction bipolar transistor (HBT) using a (Ga,In)P/GaAs heterojunction emitter on a GaAs base. This combination is of interest as a potential alternate to (Al,Ga)As/GaAs, because of theoretical predictions of a larger valence band discontinuity and a smaller conduction band discontinuity, thus eliminating the need for grading of the emitter/base junction. The structure was grown by molecular beam epitaxy, with the base doping (∼1019cm-3) far exceeding the n-type doping ∼517cm-3) of the (Ga,In)P wide gap emitter (E g = 1.88 eV). Common-emitter current gains of 30 were attained at a current density of 3000 A/cm2, the highest current density achieved without burnout.
TL;DR: In this article, the first observation of light-hole band carriers in In0.2Ga0.8As/GaAs strained-layer superlattices by direct measurements of their effective mass (m*mo=0.14) using oscillatory magnetoresistance data was reported.
Abstract: We report the first observation of light‐hole band carriers in In0.2Ga0.8As/GaAs strained‐layer superlattices by direct measurements of their effective mass (m*mo=0.14) using oscillatory magnetoresistance data. Preferential population of light‐hole states, due to splitting of the degenerate bulk valence bands by built‐in strain, allows this direct observation.
TL;DR: In this paper, the photoluminescence spectra of two GaAs/GaAs heterojunctions were analyzed and the location of the spectrum peak and shoulders agreed well with the calculated energies using Dingle's connection rule.
Abstract: Quantum‐mechanically coupled well systems consisting of two GaAs wells 30 A thick separated by an Al0.5Ga0.5As barrier whose thickness was varied from 12 to 40 A have been grown by metalorganic chemical vapor deposition. The photoluminescence spectra of these systems indicated the splitting of a degenerate single well state into a doublet state, a symmetrical state, and an antisymmetric state. The location of the spectrum peak and shoulders agreed well with the calculated energies using Dingle’s connection rule which assumes 85% conduction band offset and the continuous first derivative of the wave function across the AlGaAs/GaAs heterojunction. Two other connection rules were tried, but the agreement was worse.
TL;DR: In this article, the effect of the conduction-band spike on the offset voltage depends on the compositional grading and in properly graded devices, the effect is negligible and the negative collector current is equal to or less than the base current.
Abstract: Factors affecting the collector‐emitter offset voltage in AlGaAs/GaAs heterojunction bipolar transistors have been examined both experimentally and theoretically. In the offset region the collector current, instead of being zero as reported in the literature, is negative and is equal to or less than the base current. The majority of our double heterojunction transistors have negligible offset voltage (50 mV). The prime reason of unusually large offset voltages as observed in some of our devices is found to be the poor quality of the base‐collector (b‐c) junction which is affected by the growth and fabrication processes. The effect of the conduction‐band spike on the offset voltage depends on the compositional grading and in properly graded devices is negligible. For zero offset voltage, high quality of the b‐c junction is important such that its turn‐on voltage is either equal to or higher than that of the emitter‐base junction.