Isotype Heterojunction Research Articles

Radical assisted metalorganic chemical vapor deposition of CdTe on GaAs and carrier transport mechanism in CdTe/n-GaAs heterojunction

The growth and carrier transport mechanism in CdTe on the GaAs substrate is reported. Epitaxial layers of CdTe were grown on n- and semi-insulating GaAs substrates by the hydrogen radical assisted metalorganic chemical vapor deposition technique at a low pressure. Dimethylcadmium and diethyltelluride were used as the source materials. The growth was carried out in the substrate temperature range of 150–300 °C. The grown films have high resistivity in the order of 107 Ω cm for the entire growth range. Applicability of this heteroepitaxial CdTe layer on n-GaAs as an x-ray detector was then investigated. The carrier transport mechanism of the CdTe/n-GaAs heterojunction was studied by means of current–voltage measurements at different temperatures. The forward current was characterized by multitunneling capture-emission current and space charge limited current. The reverse current was considered as the generation current from the heterojunction interface states through the analysis of capacitance–voltage measurement. It is found that for devices using minority carriers, this heterojunction alone is not useful because of the high concentration of interface states. A suitable modification, like an isotype heterojunction between GaAs and CdTe before forming the p-n junction, seems to be necessary.

The a-SiC/c-Si(n) Isotype Heterojunction as a High Sensitivity Temperature Sensor

The a-SiC/c-Si(n) isotype heterojunction has been studied as a temperature sensor by measuring its reverse current-voltage (IR-V) and reverse voltage-temperature (V-T) characteristics, as well as its reverse current temperature dependence. The IR-V characteristics exhibit an almost constant current, whereas the reverse current Ia depends strongly on T (from 230 K up to 320K). The V-T characteristics, at different reverse currents, reveal a highly temperature sensitive behavior for the a-SiC/c-Si(n) junction. The measured values of temperature sensitivity (AV/AT) was found to be (- -2.5 V/K) in the moderate temperature range, which are much higher than those obtained with bulk semiconductor temperature sensors. The high sensitivity-temperature-range of the a-SiC/c-Si(n) heterojunctions can be controlled electrically within the regim of values from 230K up to 320 K. Finally, the high sensitivity of these devices, in conjunction with the fact that a-SiC films can be used as an add-on to the existing Si technology, emerge new possibilities to the fabrication of high sensitivity temperature microsensors.

Isotype heterojunctions with flat valence or conduction band

We show that isotype heterojunctions with a perfectly flat majority or minority carrier band edge can be realized by modulation doping of arbitrary continuous alloy grading. The required impurity distribution is obtained analytically from the knowledge of the compositional grading and band structure parameters in the grading. This analytic relationship is exact for heterojunctions in which the grading fields are negligible in comparison with the atomic fields. We illustrate the design of flat valence-band heterojunctions for application in high-reflectivity low-resistance distributed Bragg reflectors for vertical-cavity lasers. The presented formalism enables the design of isotype heterojunctions with arbitrary band-edge profiles.

InAsSb p-n junction light emitting diodes grown by liquid phase epitaxy

The liquid phase epitaxial growth technique was used to grow InAsSb p-n junctions on N-GaSb substrates from an Sb-rich solution. The electrical and optical properties of these diodes were investigated in the temperature range 80–300 K. Electroluminescence (EL) emission near 4.2 μ m was readily observed from our homojunction diodes. The effects of zinc doping on the diode electrical properties and electroluminescence quantum efficiency were also investigated. The I–V characteristics and EL efficiency of these p-n InAsSb/N-GaSb diodes were compared with those of n-InAsSb/N-GaSb isotype heterojunction diodes.

Delta-doping-enhanced InGaAs/InAlAs heterobarrierdiodes

Modification of the effective conduction-band offset in InGaAs/InAlAs isotype heterojunctions by incorporating, during epitaxial growth, a doping dipole formed by alternate n+, p+ delta (δ-) doping is demonstrated. Greatly improved current rectification is found when the dipole polarity enhances the potential barrier.

Energy-Band offsets and electroluminescence in n-InAs1-xSb1-x/N-GaSb heterojunctions grown by liquid phase epitaxy

Isotype heterojunctions of n-InAsSb/N-GaSb were grown by liquid phase epitaxy from Sb-solution. The current-voltage and capacitance-voltage characteristics of these structures were investigated. Valence band and conduction band offsets were measured to be AEv = 0.40 eV and AEc = 0.84 eV, respectively, in good agreement with theory. Electroluminescence emission at 4 am from these isotype heterojunction diodes is reported for the first time. The injection mechanisms determining luminescence efficiency are also briefly discussed.

Rectifying junctions in peripherally-substituted metallophthalocyanine bilayer films

Thin bilayer films formed by the sequential vapor deposition of two different peripherally-substituted metallophthalocyanines exhibit rectifying behavior toward an applied dc voltage. The degree of rectification is shown to be enhanced in the presence of oxygen. These bilayer films demonstrate that device activity can be imparted to a phthalocyanine junction via «band tuning» and represent the first examples of non-Schottky type rectification observed in phthalocyanine-based junctions. Analysis of the forward current-voltage characteristics suggests that a possible Frenkel-Poole carrier detrapping mechanism exists in these systems. Preliminary band structure calculations indicate that the bilayers are actually p-p isotype heterojunctions

A Study of a-Sic/C-Si(n) Isotype Heterojunctions

In the present work a study of the electrical properties of heterojunctions between rf sputtered amorphous silicon carbide (a-SiC) thin films and n-type crystalline silicon (c-Si) substrates is reported. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics, as well as the temperature dependence of the current of a-SiC/c-Si(n) heterojunctions were measured. The I-V characteristics of a-SiC/ c-Si(n) heterojunctions exhibit poor rectification properties, with a high reverse current, at higher temperatures (T > 250K), whereas good rectification properties are obtained at lower temperatures (T < 250K). It was found that the a-SiC/c-Si(n) heterojunctions are isotype, suggesting that-the conductivity of a-SiC is n-type. The temperature dependence of the current (from 185K to 320K) showed that the majority carriers of c-Si(n) (i.e. electrons) are transported from c-Si(n) to a-SiC mainly by the thermionic emission mechanism, or by the drift-diffusion mechanism. From C-V measurements of a-SiC/c-Si(n) heterojunctions the electron affinity of a-SiC was found to be X1= 4.20 ± 0.04 eV. Finally, the a-SiC/ c-Si(n) isotype heterojunctions are expected to be interesting devices as infrared

Characteristics of mesa- and LOCOS-isolated molecular beam epitaxy SiGe diodes

Molecular beam epitaxy grown p+–n SiGe–Si heterojunction diodes with and without p+Si caps on top of the p+ SiGe have been fabricated on n-type Si<100> wafers with and without SiO2 LOCOS patterns. It is shown that the p+Si caps create p+–p+ Si–SiGe isotype heterojunctions in series with the p+–n SiGe–Si heterojunctions. Potential barriers and carrier depletion regions exist in the isotype heterojunction regions owing to the band-gap difference between the two materials. Effects of the LOCOS and the p+–p+ Si–SiGe isotype heterojunction in series with the p+–n SiGe–Si heterojunction on the characteristics of the diodes were studied experimentally and using simulation. The diodes fabricated exhibited I–V characteristics ideality factors between 1.05 and 1.20.

Numerical modelling of carrier profiles in isotype and anisotype heterojunction devices

Device optimization and measurement evaluation require accurate modelling of carrier distributions and related C- V characteristics. Here a powerful numerical modelling procedure for Schottky-contacted isotype heterostructures[1] is reviewed and used as a starting point for important extensions, which comprise the evaluation of p- n structures, the inclusion of thin counterdoped layers and the recharging of spatially distributed interface states across junction boundaries. The results obtained are checked successfully against analytical calculation procedures.

Low-temperature C-V characteristics of Si-doped Al0.3Ga0.7As and normal n-GaAs/N-Al0.3Ga0.7As isotype heterojunctions grown via molecular beam epitaxy

C-V measurements on normal isotype GaAs/Al0.3Ga0.7As heterojunctions grown via molecular beam epitaxy were undertaken in the temperature ranges between 300 and 4.2 K. For temperatures ≤100 K, we found a persistent conductivity effect due to the field emitted and then capture delayed electrons in the Si-doped Al0.3Ga0.7As layer. These capture-delayed free carriers lead to apparent increase of the base doping in the AlGaAs and consequent reappearance of the valley in the concentration-versus-distance profiles of the heterojunctions at temperatures ≤100 K. The resultant temperature dependence of the calculated conduction-band offsets and the interface-state densities were found to be an artefact. Apparent shifting of the heterointerface positions observed in inverted heterojunctions was not observed in the normal GaAs/AlGaAs heterojunctions. The normal heterostructure enabled us to distinguish and determine the concentration of each deep donor level.

On the numerical simulation of C-V measurements at isotype and anisotype heterojunctions

On the numerical simulation of C-V measurements at isotype and anisotype heterojunctions

Deep levels in Te-doped AlSb grown by molecular beam epitaxy

Deep electron traps in Te-doped AlSb have been investigated by deep level transient spectroscopy (DLTS). The diodes used for DLTS measurement were InAs/AlSb n-N isotype heterojunctions (quasi-Schottky barriers) with excellent rectification characteristics, grown on n+-GaAs substrates by molecular beam epitaxy. In the temperature range investigated, from 90 to 300 K, a number of electron trap levels were observed, not all of them well defined. The best-defined level was found to have a thermal electron emission energy of 0.26 eV, much shallower than the values 0.46–0.48 eV found by Takeda et al. for AlxGa1−xSb alloys with x≤05. This suggests a compositional dependence of the thermal emission energy for the deep electron trap level in AlxGa1−xSb in the range 0.4<x≤1.0, in contrast to the constant value reported for AlxGa1−xAs. Temperature-dependent Hall effect measurements gave an ionization energy of 100 meV, suggesting that EDX decreases with increasing Al content, as in (Al,Ga)As. In a sample doped with Te at a level of 3.1×1017 cm−3, the trap concentration was 2.0×1017 cm−3, indicating that Te-doped AlSb has a much larger number of deep electron traps than n-AlAs.

The performance of doping interface dipoles in heterostructures

The modulation of the potential barrier of an isotype heterojunction by the incorporation during epitaxial growth of thin, heavily doped n and p regions either side of the heterointerface has been investigated by computer modelling. The resulting device structure, known as a doping interface dipole or DID, was first proposed by Capasso and co-workers (1985) as a means of introducing a bias-dependent pseudo-band offset in heterojunction devices. The results presented here predict how this bias dependence varies with the doping dipole parameters and the material properties of the host heterojunction, chosen here to be a pseudomorphic Si1-xGex/Si p-isotype heterojunction.

C–V Measurements of Isotype Heterojunctions with Deep Rechargeable Interface States

physica status solidi (a)Volume 120, Issue 1 p. K53-K56 Short Note C–V Measurements of Isotype Heterojunctions with Deep Rechargeable Interface States W. Pittroff, W. Pittroff Zentralinstitut für Optik und Spektroskopie der Akademie der Wissenschaften der DDR, Berlin Search for more papers by this author W. Pittroff, W. Pittroff Zentralinstitut für Optik und Spektroskopie der Akademie der Wissenschaften der DDR, Berlin Search for more papers by this author First published: 16 July 1990 https://doi.org/10.1002/pssa.2211200138Citations: 2 Rudower Chaussee 6, DDR-1199 Berlin, GDR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume120, Issue116 July 1990Pages K53-K56 RelatedInformation

Numerical modeling of heterojunctions including the thermionic emission mechanism at the heterojunction interface

A numerical model for heterojunctions is discussed in which current transport across the heterojunction interface is taken into account by using thermionic emission current in series with drift-diffusion current in the bulk. The thermionic emission current is regarded as a boundary condition, which is used to obtain a relationship between quasi-Fermi-levels on both sides of the interface. GaAs-AlGaAs heterojunctions are simulated as an example, and the results are compared with those obtained by a conventional diffusion model in which current transport across the heterojunction interface is not considered explicitly. It is shown that the thermionic emission mechanism is important and should be considered, particularly in isotype heterojunctions. With the present model, more general numeral analyses that include thermionic emission, drift, and diffusion phenomena can be achieved. >

HgCdTe all-epitaxial semiconductor/semimetal Schottky photodiode

We propose and demonstrate an all-epitaxial semiconductor/semimetal Schottky (S3) photodiode based on an n-type Hg0.56Cd0.46 Te/HgTe isotype heterojunction. The structure, grown using molecular beam epitaxy, was fabricated into back-illuminated mesa diodes. A 40-μm-diam photodiode shows room-temperature rectification and high efficiency photoresponse, with a long-wavelength cutoff of 2.43 μm and a peak quantum efficiency of 44% at 2.0 μm for 250 mV of reverse bias. The dark current at this bias is 100 μA.

On the generalized diffusion theory of current transport in isotype heterojunctions

The generalized diffusion theory of current transport inn-n isotype heterojunctions enunciated previously has been extended to the realistic case of there being two different electron mobilities in the two semiconductors forming then-n heterojunction. This extended theory too reduces to the diffusion theory of current in metal-semiconductor contacts under the appropriate limiting conditions in the same way as the previous theory does. The current-voltage characteristics forn-n heterojunctions according to this extended theory would be different from those according to the previous theory if the values of all the parameters involved such as ΛnnC, ψD1, ψD2,V1,V2, etc. could be calculated rigorously. However, utilizing the values of some parameters such as Λnn andC calculated by means of approximate expressions derived under these limiting conditions, one would evaluate current-voltage characteristics that are the same as in the previous theory. A single curve representing the current-voltage characteristic of any particularn-n isotype heterojunction can also be plotted by using a formula derived previously under zero-current conditions, in conjunction with the appropriate expressions derived in the present paper. In appendix B an alternative expression for the current density in an-n isotype heterojunction is also derived in the framework of the generalized diffusion theory.

Electrical properties and band offsets of InAs/AlSb n-N isotype heterojunctions grown on GaAs

The MBE growth and selected properties of InAs/AlSb n-N isotype heterojunctions on n+-GaAs substrates are described. Because of a large conduction-band offset (1.35 eV), these junctions behave like Schottky barriers, with excellent rectification characteristics, despite the presence of a very high density (>107 cm−2) of threading dislocations resulting from the large lattice mismatch (7%) between AlSb and the GaAs substrate. The forward I-V characteristics, corrected for series resistance, exhibit a large nonideality factor of about 1.8, suggesting that the main current flow is along a defect path, presumably related to the misfit dislocations. Reverse C-V characteristics exhibit a perfectly linear 1/C2 vs V plot, from which a conduction-band offset of 1.35±0.05 eV is deduced. This value is in excellent agreement with the value predicted from the known band offsets in InAs/GaSb and GaSb/AlSb.

Determination of free carrier concentration profiles and the valence-band discontinuity energy of Hg0.7Cd0.3Te/Cd(4% Zn)Te heterojunctions using organic semiconductor layers

Capacitance-voltage data are utilized to obtain the free-carrier concentration in n- and p-type Hg1−yCdyTe layers, and to measure the valence-band discontinuity energy of a p-type Hg0.7Cd0.3Te/Cd(4% Zn)Te isotype heterojunction. To facilitate measurement, rectifying contact was made to the Hg1−yCdyTe layers using one of two organic materials—metal-free phthalocyanine and copper phthalocyanine. Contrary to previous results with this heterojunction system, we find that holes are accumulated near the Cd(4% Zn)Te side (rather than Hg1−yCdyTe side). We obtain a valence band discontinuity energy (ΔEv ) equal to (110±20) meV, and a fixed interface charge density of σ=−(5.9±0.3)×1010 cm−2.