Exciton emission from forward-biased zinc selenide Schottky diodes

Exciton emission has been observed in the forward-biased electroluminesence of ZnSe Schottky diodes free of intentionally added luminescent centres. The emission has been studied from ≈ 95° K to room temperature and is attributed to the recombination of free excitons (zero-LO phonon line). No LO phonon side bands were observed. As with exciton photoluminescence in CdS the half-width of the emission line, although a linear function of temperature, is greater than that predicted by theory. At temperatures below ≈150°K pair emission was also observed.     

High reliability sputtered Schottky diodes on GaAs

We describe developments to improve reliability and power handling for high frequency applications in whisker-contacted Schottky barrier diode mixers, detectors and multipliers fabricated using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSi_x/GaAs contacts respectively.     

Investigation of GaAs Schottky barrier diodes in the THz range

The properties of GaAs Schottky barrier diodes as video detectors and mixing elements were investigated in the frequency range from 0.8–2.5 THz. For the most sensitive diode, the video responsivity and system noise temperature were measured as a function of incident laser power. The highest video responsivity was 2,000 V/W at 214m and 60 V/W at 118m. For five diodes differing in doping, capacitance, series resistance and anode diameter, the system noise temperature was measured at 214m and 118m. The best single sideband (SSB) values are 12,300 K and 24,200 K at 214m and 118m, respectively. The system noise temperature versus frequency is given over the range from 0.5–3 THz for two specific diodes demonstrating that the sharpness of the I–V characteristics is only of secondary importance for mixer perfomance at such high frequencies.     

Thermally stimulated currents in semi-insulating GaAs Schottky diodes and their simulation

We report the investigation of the non-irradiated and irradiated-with-pions Schottky diodes made on semi-insulating GaAs. Thermally stimulated currents have been measured experimentally and modeled numerically. To reveal the influence of the single levels, we used the thermal emptying of the traps by fractional heating. Attention is paid to the comparative analysis of the distribution of the parameters of different samples produced and processed by the same technique, contrary to the usual approach of the analysis of a few different samples. The following main conclusions are drawn. First of all, many different levels (from 8 to 12) have been found in the temperature range from 90 K to 300 K in all samples. Their activation energies range from 0.07 up to 0.55 eV, their capture cross-sections are 10^-22–10^-14 cm², and initial occupation is 2×10¹¹–5×10¹⁴ cm^-3. The irradiation with pions does not influence the density of most levels significantly. On the other hand, levels with activation energies of about 0.07–0.11 eV, 0.33–0.36 eV, 0.4–0.42 eV, and 0.48–0.55 eV have been found only in the irradiated samples. Irradiation also increases the inhomogeneity of the crystals, which causes the scattering of the activation energies obtained by fractional heating technique. Received: 13 November 1998 / Accepted: 16 April 1999 / Published online: 4 August 1999     

Free exciton emission in forward-biased CdS MIS diodes

The radiative decay of free excitons with the emission of 0, 1, or 2LO phonons has been observed in electroluminescence in Cds MIS diodes operated in forward bias at temperatures in the range 40 – 77K. The line shapes and temperature dependence of the ILO and 2LO phonon assisted replicas are discussed in terms of the distribution of kinetic energy of the excitons with an effective temperature equal to that of the lattice.     

Prediction of lateral barrier height in identically prepared Ni/n-type GaAs Schottky barrier diodes

We have identically prepared Ni/n-GaAs/In Schottky barrier diodes (SBDs) with doping density of 7.3 × 10¹⁵ cm⁻³. The barrier height for the Ni/n-GaAs/In SBDs from the current-voltage characteristics have varied from 0.835 to 0.856 eV, and ideality factor n from 1.02 to 1.08. We have determined a lateral homogeneous barrier height value of 0.862 eV for the Ni/n-GaAs/In SBD from the experimental linear relationship between barrier heights and ideality factors.     

Spin dependent conductivity and photovoltage in ZnSe:Mn2+ Schottky barrier diodes

Light emitting ZnSe:Mn²⁺ Schottky barrier diodes have been investigated by magnetic resonance and for the first time a deep centre resonance, Mn²⁺, has been observed by monitoring the forward and reverse conductivity. In the same experiments a donor resonance was also observed as an increase in conductivity. Using two ohmic contacts the Mn²⁺ resonance and a hole centre resonance, most probably a (V_Zn-Cl) acceptor, were recorded by monitoring the photoconductivity. The Mn²⁺ could also be detected in the photovoltaic signal. These experiments suggest new techniques to investigate deep centres in semiconductors.     

Magnetic properties of MnAs nanocrystals embedded in GaAs

A phenomenological model for explaining the magnetic properties of MnAs nanocrystals embedded in GaAs is proposed. It is shown that experimental data of DC magnetization as a function of temperature, obtained according to zero-field-cooled and field-cooled protocols, can be understood assuming a transition of the system from a low temperature state in which very slow dynamics is observed (frozen state) to a high-temperature state in which dynamics is fast (quasi superparamagnetic state).     

Spectroscopic measurement of spin-dependent resonant tunneling through a 3D disorder: the case of MnAs/GaAs/MnAs junctions

We propose an analytical model of spin-dependent resonant tunneling through a 3D assembly of localized states (spread out in energy and in space) in a barrier. An inhomogeneous distribution of localized states leads to resonant tunneling magnetoresistance inversion and asymmetric bias dependence as evidenced with a set of experiments with MnAs/GaAs(7-10 nm)/MnAs tunnel junctions. One of the key parameters of our theory is a dimensionless critical exponent beta scaling the typical extension of the localized states over the characteristic length scale of the spatial distribution function. Furthermore, we demonstrate, through experiments with localized states introduced preferentially in the middle of the barrier, the influence of an homogeneous distribution on the spin-dependent transport properties.     

Potential barrier inhomogeneities in irradiated Pd/n-SiGe Schottky diodes

Ion implantation, which is an important process in the fabrication of microelectronic devices, is known to have a strong impact on the electrical performance of materials and devices [1]. In this context we study the temperature-dependence of parameters relevant to Pd/Si_0.9Ge_0.1/Si Schottky diodes subjected to He⁺ ion implantation. The irradiated Pd/SiGe junction is linearly graded as evidenced by the capacitance–voltage data but the temperature dependence of the diode’s ideality factor and barrier height is similar to behavior reported for abrupt junctions. The observed trends, usually described as anomalies, can not be fully explained by considering the combined effects of tunneling, recombination, image-force lowering and/or series resistance. It is shown, however, that when taking barrier height non-homogeneity into account the experimental results can be satisfactorily explained. The barrier height is seen to follow a Gaussian distribution with a mean barrier of 0.8 eV and with a standard deviation that appears to be dependent on voltage and also weakly on temperature. It is suggested that the potential barrier deformation itself is temperature dependent at a given bias-voltage with the deformation becoming relatively more pronounced at lower temperatures. PACS 85.30.Hi; 73.30.+y; 73.40.V     

Noise reduction in sputtered W/GaAs Schottky junctions

The noise characteristics of sputtered W/GaAs Schottky diodes, annealed at temperatures up to 700°C, have been investigated. A useful figure of merit for such millimeter and submillimeter mixer diodes is the noise performance at an RF where accurate measurements are available. Noise temperatures measured at a typical mixer intermediate frequency of 4GHz under DC biased conditions have been reduced significantly by rapid thermal annealing. The best noise data have been obtained with an annealing time of 2 minutes at 600°C and are consistent with good mixer performance.     

Fabrication and analysis of GaAs Schottky barrier diodes fabricated on thin membranes for terahertz applications

The GaAs Schottky diode is predominantly used as the critical mixer element in heterodyne receivers in the frequency range from 300 GHz to several THz[1]. At operating frequencies above one THz the skin effect adds significant parasitic resistance to the diode which degrades the receiver sensitivity. A novel diode structure called the Schottky barrier membrane diode is proposed to decrease the skin effect resistance by reducing the current path between the Schottky and ohmic contacts. This is accomplished by fabricating the diode on a very thin membrane of GaAs (about 1 m thickness). A theoretical analysis has shown that this will reduce the substrate resistance by 60% at 3 THz. This reduction in resistance corresponds to a better frequency response which will improve the device's performance as a mixer element.This work has been supported by a grant from Texas Instruments and the National Science Foundation under contract ECS-8412477     

Design and fabrication of 0.5 micron GaAs Schottky barrier diodes for low-noise terahertz receiver applications

Recent technological advances have made possible the development of heterodyne receivers with high sensitivity and high spectral resolution for frequencies in the range 1,000–3,000 GHz (1–3 THz). These receivers rely on GaAs Schottky barrier mixer diodes to translate the high-frequency signal to a lower frequency where amplification and signal processing are possible. At these frequencies, the diode quality is a major limitation to the performance of the receiver. The design, fabrication and DC evaluation of a diode for this frequency range is presented. A figure-of-merit cut-off frequency of over 10 THz is achieved with a record low zero biased capacitance of 0.5 fF. Results from RF tests are also given.This work has been supported in part by the National Science Foundation under contract ECS-8720850 and the US Army.     

Temperature dependent electrical characteristics of Sn/p-Si Schottky diodes

Current-voltage and capacitance-voltage characteristics of Sn/p-Si Schottky diodes measured in the temperature range 80-320 K are presented and analysed. Anomalous strong temperature dependencies of the ideality factor and apparent barrier height were obtained. There was also a considerable difference between the apparent barrier heights obtained from current-voltage and capacitance-voltage characteristics. These anomalies are explained by the domination of the current by a high level of thermionic-field emission, and by the presence of deep levels near the Sn/Si interface, which yield a reduction of free hole concentration and a significant temperature dependence of the charge stored near the metal-semiconductor (MS) interface. The evaluation of temperature dependence of forward current for thermionic-field emission resulted in the following parameters: characteristic energy E₀₀ = 9.8 meV, Schottky barrier height at zero bias Φ_b0 = 0.802 eV, bias coefficient of barrier height β = 0, and effective Richardson constant A* = 37.32 A cm⁻² K⁻².     

Unforeseen properties of MnAs epilayers grown on GaAs semiconductor

This paper reviews some recent works performed on MnAs/GaAs thin films and other related structures grown by molecular beam epitaxy. The impact of epitaxy on the magneto-structural properties of MnAs and possible applications of MnAs epilayers are discussed. A brief account of recent results obtained on the magneto-transport in MnAs/GaAs/MnAs magnetic tunnel junctions is also given, highlighting several appealing and promising properties of this system for spintronics applications.     

Barrier height modification in Schottky MIS diodes

Expressions for the potential barrier height of Schottky MIS diodes having gaussian doping profiles are derived and solved numerically both at thermal equilibrium and in the presence of applied voltages. The possibility of barrier height modification using a thin highly doped surface layer is discussed.     

Intersecting behaviour of nanoscale Schottky diodes I-V curves

We describe a new feature connected with Schottky barriers with nanosize dimensions. We found out by theoretical analysis that the I-V curves of such small diodes measured at different temperatures should intersect and consecutively at higher voltages larger current flows through the diode at lower temperatures. This effect which is at first glance in contradiction with the thermionic theory is caused by the series resistance influence. We show that the presence of the series resistance is a necessary condition of its observation. However, the intersection voltage—minimum voltage at which the intersection may occur—increases with the value of the series resistance and the diode dimensions for which the effect could be observable in Si diodes and the common series resistance values must be in submicrometer range. Diodes with several hundreds nanometers dimension have the intersection voltage ∼1 V. Analytical expression for the intersection voltage values was also derived.     

Determination of the series resistance under the Schottky contacts of AlGaN/AlN/GaN Schottky barrier diodes

Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) were fabricated,and the gate and the source of the HFETs consisted of AlGaN/AlN/GaN Schottky barrier diodes (SBDs).Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs,the series resistance under the Schottky contacts (RS) was calculated using the method of power consumption,which has been proved to be valid.Finally,the method of power consumption for calculating R S was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs.It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AlGaN/AlN/GaN SBDs and the AlGaN/AlN/GaN HFETs.     

Determination of the series resistance under the Schottky contacts of AlGaN/AlN/GaN Schottky barrier diodes

Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) were fabricated, and the gate and the source of the HFETs consisted of AlGaN/AlN/GaN Schottky barrier diodes (SBDs). Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs, the series resistance under the Schottky contacts (R_S) was calculated using the method of power consumption, which has been proved to be valid. Finally, the method of power consumption for calculating R_S was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs. It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AlGaN/AlN/GaN SBDs and the AlGaN/AlN/GaN HFETs.