Epitaxial Diodes Research Articles

Optically pumped transport in ferromagnet-semiconductor Schottky diodes (invited)

Optical pumping is used to generate spin-polarized carriers in epitaxial ferromagnet-GaAs Schottky diodes with InyGa1−yAs quantum wells placed in the depletion region. A strong dependence of the photocurrent on the polarization state of the incident light is observed, and a series of measurements as a function of excitation energy, bias voltage, magnetic field, and excitation geometry are used to distinguish spin-dependent transport from a variety of background effects. The spin polarization of the photocurrent for pumping energies at and above the band gap of GaAs is of order 0.5% or less. Much larger polarization dependence is observed for excitation energies near the quantum well ground state. Although background effects are very large in this regime, the field dependence of the polarization signal for several samples is suggestive of spin-dependent transport.

Investigation on the charge collection properties of a 4H-SiC Schottky diode detector

We present experimental and theoretical data on the charge collection properties of a 4H-SiC epitaxial Schottky diode exposed to 5.48- and 2.00-MeV alpha particles. Hundred percent Charge Collection Efficiency (CCE) is, in particular, demonstrated for the 2.00-MeV alpha particles at reverse voltages higher than 40 V . By comparing measured CCE values with the outcomes of drift-diffusion simulations, a value of 500 ns is inferred for the hole lifetime within the lowly doped, active layer of virgin samples. The contributions of diffusion and funneling-assisted drift to CCE at low reverse voltages are pointed out.

Deep-level transient spectroscopy studies of silicon detectors after 24 GeV proton irradiation and 1 MeV neutron irradiation

Deep-Level Transient Spectroscopy (DLTS) has been used to investigate the defects in high-resistivity silicon detectors after 1×10 11 proton cm −2 irradiation at room temperature. The ( E c−0.43±0.02) eV peak is seen in all materials after irradiation by neutrons or protons and has been investigated carefully. Annealing experiments show that it consists of four individual defects, one of which is the single negative divacancy. Two defects ( E c−0.35±0.02) eV and ( E c−0.45±0.03) eV anneal out at 70°C. A level ( E v+0.20±0.02) eV was also observed to anneal out at about 60°C in a p-type epitaxial diode after neutron irradiation. We propose that these levels can be identified as to be V 3 + ( E v+0.20±0.01) eV, V 3 − ( E c−0.45±0.03) eV and V 3 −− ( E c−0.35±0.02) eV charge states of the trivacancy, V 3. A defect at ( E c−0.37±0.02) eV annealed out at 170°C and may be the four vacancy, V 4.

Ballistic electron emission microscopy studies of the temperature dependence of Schottky barrier height distribution in CoSi 2/n-Si(1 0 0) diodes formed by solid phase reaction

Ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy have been performed on polycrystalline and epitaxial CoSi 2/n-Si(1 0 0) contacts at temperatures ranging from −144°C to −20°C. The ultra-thin CoSi 2 films (∼10 nm) were fabricated by solid state reaction of a single layer of Co (3 nm) or a multilayer of Ti (1 nm)/Co (3 nm)/amorphous-Si(1 nm)/Ti (1 nm) with a Si substrate, respectively. The spatial distribution of barrier height over the contact area obeys a Gaussian function at each temperature. The mean barrier height increases almost linearly with decreasing temperature with a coefficient of −0.23±0.02 meV/K for polycrystalline CoSi 2/Si diodes and −0.13±0.03 meV/K for epitaxial diodes. This is approximately equal to one or one-half of the temperature coefficient of the indirect energy gap in Si, respectively. It suggests that the Fermi level is pinned to different band positions of Si. The width of the Gaussian distribution is about 30–40 meV, without clear dependence on the temperature. The results obtained from conventional current–voltage and capacitance–voltage ( I– V/ C– V) measurements are compared to BEEM results.

Visible light-emitting diodes grown on optimized ∇x[InxGa1−x]P/GaP epitaxial transparent substrates with controlled dislocation density

Epitaxial transparent-substrate light-emitting diodes (ETS-LEDs) have been fabricated on optimized graded buffers of InxGa1−xP on GaP (∇x[InxGa1−x]P/GaP) that feature controlled threading dislocation densities of 3×106 cm−2. The ETSLEDs show increasing efficiency from 575 nm to 655 nm, in marked contrast to previous reports where performance drops above 600 nm, and feature the lowest spectral widths ever reported in ∇x[InxGa1−x]P/GaP. The improvement over earlier reports is attributed to large mean dislocation spacings in optimized ∇x[InxGa1−x]P/GaP, which are an order of magnitude greater than the mean carrier diffusion length. A slight performance decline remains at 655 nm, but the overall performance of this first generation of ETS-LEDs is promising.

Electroluminescence From Implanted and Epitaxially Grown pn-Diodes

The electroluminescence from pn-diodes with (1) aluminum doped epitaxially grown, (2) aluminum implanted or (3) aluminum and boron implanted p-layer have been investigated. The temperature dependence for both the spectra and the decays of the major spectral components have been investigated at temperatures from 80 K to 550 K. The implanted diodes show implantation damage in the form of the D-1 center and lack of emission from the aluminum center. The epitaxial diodes show luminescence from the aluminum center. The band edge luminescence is visible above 150 K for the epitaxial diode and above 300 K for the implanted. The emission from deep boron can be seen in the aluminum and boron co-implanted diode and in the epitaxially grown diode that have an unintentional boron doping below 10(17) cm(-3).

Characteristics of an epitaxial Schottky barrier diode for all levels of injection

The effect of the minority carrier recombination on injection ratio and charge storage time of an epitaxial Schottky barrier (SB) diode has been presented. The dependence of injection ratio and storage time on the minority carrier reflecting properties of the epitaxial-substrate interface is also studied when the drift region of a SB diode is fully invaded by the minority carriers. The study shows that at a relatively low current density, the conductivity modulated region partially occupies the drift region and the charge stored within the injection region cannot be neglected. In the present work, this region is considered for the first time in studying the characteristics of the SB diode. Analytical expressions for the diode forward current, minority carrier injection ratio and storage time parameters are obtained; and the derived expressions are applicable for all levels of injection. In the previous works, to model the complete range of injection level in the SB diode, empirical formulas were introduced to combine the high-level injection model with the traditional low-level current–voltage equations.

Characterisation of deep level trap centres in 6H-SiC p-n junction diodes

Deep level transient spectroscopy (DLTS) measurements were performed on silicon carbide (6H-SiC) n +p −p + junction diodes in order to compare the electrical properties and quality of epitaxial layers in the implanted and the epitaxial emitter diodes, where the p −p + layers are the same. Four hole trap centres were detected on the implanted emitter diodes. Their thermal activation energy’s are 0.49, 0.6, 0.7 and 0.87 eV, respectively, referred to the valence band. The last three trap centres are also observed on the epitaxial emitter diodes. The origin of deep levels, with E a=0.7 and 0.87 eV, is still under investigation. The thermal activation energy and capture cross section (0.6 eV, 4.3×10 −15 cm 2) is in good agreement with values reported for the boron-related D-centre. The trap centre with E a=0.49 eV is associated to the ion-implantation process of the n + layer. Double deep level transient spectroscopy measurements (DDLTS) have been performed to accurately profile this last defect through the depletion region. Its trap concentration N T( x) as a function of the depletion region width indicates that this defect is located near the n +/p − junction.

Effects of surface defects on the performance of 4H– and 6H–SiC pn junction diodes

Effects of surface defects on performance of kV-class 4H– and 6H–SiC epitaxial mesa pn junction diodes were investigated. Mapping studies of surface morphological defects have revealed that triangular-shaped defects severely degrade high-blocking capability of the diodes whereas shallow round pits and scratch give no direct impact. The perimeter recombination and generation, instead of the bulk process, are responsible for forward recombination current and reverse leakage current of the diodes, respectively. Effective minority carrier lifetimes are mainly limited not by bulk recombination but by perimeter recombination.

Effect of laser radiation on GaP epitaxial diode structures

The effect of laser radiation on the current-voltage characteristics and intrinsic quantum yield of electroluminescence after irradiation is investigated. As a result of irradiation at supercritical radiant power flux levels (greater than 107 W/cm2) an abrupt drop in the luminescence quantum yield and a steep growth of the leakage currents are observed in the current-voltage characteristics. It is assumed that by exciting the electronic subsystem of the impurity atoms the powerful optical radiation facilitates the occurrence of quasichemical reactions.

Irradiation tests of photodiodes for the ATLAS SCT readout

Two kinds of photodiodes have been investigated for the ATLAS SCT readout. We present in this paper the results of irradiating bulk and epitaxial Si PIN diodes with 1 MeV-equivalent neutrons and 24 GeV protons. The devices were biased during some of the tests. They were exposed to a fluence of around 2.5 × 10 14 n cm −2 followed by a fluence of approximately 2.5×10 14 p cm −2.

Infrared response of epitaxial and polycrystalline CoSi2 Schottky diodes

The influence of grain boundary scattering of excited carriers in CoSi2/Si Schottky diodes has been investigated by measuring the infrared response of epitaxial and polycrystalline silicide films on Si(100). An improvement in the quantum efficiency of polycrystalline diodes has been observed for thick silicide films, indicating that carriers are scattered at the grain boundaries of the silicide. The polycrystalline diodes show a quantum efficiency twice that of epitaxial detectors. The Schottky barrier height has been measured by different methods, and a difference of only a few meV is observed between the polycrystalline and the epitaxial diodes.

Temperature dependence of avalanche breakdown for epitaxial diodes in 4H silicon carbide

The temperature dependence of avalanche breakdown is investigated for uniform and microplasma-related breakdown in epitaxial 4H SiC p-n junctions. P-n mesa diodes fabricated with positive angle beveling and oxide passivation can withstand temperatures of up to 300–400 °C in the breakdown regime. Uniform avalanche breakdown in 4H silicon carbide appears to have a positive temperature coefficient, in contrast to the 6H polytype, where the temperature coefficient is negative. The influence of deep levels on avalanche breakdown in epitaxial diodes is of minor importance for uniform breakdown, but appears to be significant for breakdown through microplasmas. A negative temperature coefficient for the avalanche breakdown voltage can be observed even for 4H SiC if the breakdown is dominated by microplasmas.

Effect of doping on the forward current-transport mechanisms in a metal–insulator–semiconductor contact to InP:Zn grown by metal organic vapor phase epitaxy

A detailed study of the effect of doping density on current transport was undertaken in Au metal–insulator–semiconductor (MIS) contacts fabricated on Zn-doped InP layers grown by metal organic vapor phase epitaxy. A recently developed method was used for the simultaneous analysis of the current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics in an epitaxial MIS diode which brings out the contributions of different current-transport mechanisms to the total current. I– V and high-frequency C– V measurements were performed on two MIS diodes at different temperatures in the range 220–395 K. The barrier height at zero bias of Au/InP:Zn MIS diodes, φ 0 (1.06 V±10%), was independent both of the Zn-doping density and of the surface preparation. The interface state density distribution N ss as well as the thickness of the oxide layer (2.2±15% nm) unintentionally grown before Au deposition were independent of the Zn-doping concentration in the range 10 16< N A<10 17 cm −3; not so the effective potential barrier χ of the insulator layer and the density of the mid-gap traps. χ was much lower for the highly-doped sample. Our results indicate that at high temperatures, independent of the Zn-doping concentration, the interfacial layer-thermionic (ITE) and interfacial layer-diffusion (ID) mechanisms compete with each other to control the current transport. At intermediate temperatures, however, ITE and ID will no longer be the only dominant mechanisms in the MIS diode fabricated on the highly-doped sample. In this case, the assumption of a generation–recombination current permits a better fit to the experimental data. Analysis of the data suggests that the generation–recombination current, observed only in the highly-doped sample, is associated with an increase in the Zn-doping density. From the forward I– V data for this diode we obtained the energy level (0.60 eV from the conduction band) for the most effective recombination centers.

Parameters of epitaxial light-emitting diode structures and the features of their charge center distribution

The presence of compensated regions at the boundary of the p—n junction is established by measuring the distribution of the effective charge-center density in the space-charge region of semiconducting structures. The effect of these regions on the parameters of the capacitance-voltage characteristics and the features of the technological structure of light-emitting diodes are described.

Impact of The ge Content on The Radiation Hardness of Hetero-Junction Diodes in Sige Strained Layers

AbstractThe degradation of the electrical performance of strained Si1-xGex epitaxial diodes by 220-MeV carbon particles is reported and compared with the effect of 20-MeV alpha rays and 20-MeV protons. The macroscopic damage is studied in a broad fluence range and for different Ge contents, ranging from 8 to 16 %. It is shown that the radiation damage of carbon irradiated diodes is about one order of magnitude larger than that for alpha ray irradiation, which can be explained by considering the difference of the nonionizing energy loss (NIEL). It is observed that the reverse current at a fixed bias increases with increasing fluence, while the rate of increase decreases with increasing fluence and/or Ge content. The fact that a close to square root dependence exists between the boron deactivation in the diode depletion region, derived from capacitance-voltage measurements and the reverse current increase suggests that the device degradation is dominated by radiation induced deep levels associated with interstitial boron complexes.

Lattice Defects in Si&lt;sub&gt;1-x&lt;/sub&gt;Ge&lt;sub&gt;x&lt;/sub&gt; Epitaxial Diodes Induced by 20-MeV Alpha Rays

Lattice Defects in Si&lt;sub&gt;1-x&lt;/sub&gt;Ge&lt;sub&gt;x&lt;/sub&gt; Epitaxial Diodes Induced by 20-MeV Alpha Rays

A self-consistent technique for the analysis of the temperature dependence of current–voltage and capacitance–voltage characteristics of a tunnel metal-insulator-semiconductor structure

A new formalism is reported for the analysis of the current–voltage (I–V) characteristics of a tunnel metal-insulator-semiconductor (MIS) device, which considers a bias dependent distribution of interface states and barrier lowering due to the image force. Our theoretical expression for the I–V characteristics is general in the sense that it is applicable even under conditions when both the thermionic emission and the diffusion mechanisms of current transport compete with each other. The method is ideal for new epitaxial materials and devices where the carrier density is not known precisely beforehand. A self-consistent method of analysis is reported to determine the characteristic parameters of MIS diodes, using simultaneously the I–V and capacitance–voltage data as a function of temperature. This computational analysis has been used to examine the current transport mechanism in an Au/p-InP epitaxial MIS diode. The experimental verification of the theory and computational analysis is done by comparing the values of the interface state density distribution in thermal equilibrium with the semiconductor Nss, obtained from the forward I–V characteristics, with those directly measured by the multifrequency admittance method. Excellent agreement from these comparisons strongly supports the validity of the theory. Over the temperature range of 200–393 K, our results indicate that the interfacial layer-thermionic emission was clearly the dominant mechanism of the forward current transport in an MIS fabricated on a lightly doped InP:Zn epitaxial layer. The transmission coefficient through the insulator layer obtained from the reverse I–V characteristics was θp=1.43×10−3±7% from which we estimate an oxide thickness of 2.2 nm. The analysis of the barrier height φb0 versus temperature, obtained from 1 MHz C–V data provided a value φ0=1.06 V±10% for the zero bias and zero temperature barrier height.

Degradation and recovery of proton irradiated Si/sub 1-x/Ge/sub x/ epitaxial devices

Irradiation damage in n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x//n-Si epitaxial diodes and heterojunction bipolar transistors (HBTs) by protons is studied as a function of germanium content, proton fluence and energy for the first time. The degradation of the electrical performance of devices increases with increasing fluence, while it decreases with increasing germanium content and energy. The induced lattice defects in the Si/sub 1-x/Ge/sub x/ epitaxial layers and the Si substrate are studied by DLTS methods. In the Si/sub 1-x/Ge/sub x/ epitaxial layers for diodes, electron capture levels associated with interstitial boron complex are induced by irradiation, while two electron capture levels corresponding to the E center and the divacancy are observed in the collector region of the HBTs. The influence of the radiation source on device degradation is then discussed taking into account the number of knock-on atoms and the nonionizing energy loss (NIEL). The radiation source dependence of performance degradation is attributed to the difference of mass and the probability of nuclear collision for the formation of lattice defects. In order to examine the recovery behavior, isochronal thermal annealing is carried out for temperatures ranging from 75 to 300/spl deg/C. Based on the recovery of electrical performance, it is pointed out that the electron capture levels induced in the Si/sub 1-x/Ge/sub x/ epitaxial layers are mainly responsible for the increase of reverse diode current.

Degradation of Si1−xGex epitaxial devices by proton irradiation

Irradiation damage in n+-Si/p+-Si1−xGex/n-Si epitaxial diodes and heterojunction bipolar transistors by protons is studied. The degradation of the performance increases with increasing proton fluence, whereas it decreases with increasing germanium content and proton energy. The damage coefficient for proton irradiation is nearly the same as for neutron irradiation and is about three orders of magnitude larger than that for electron irradiation. This difference is due to the different number of knock-on atoms and the nonionizing energy loss, which is correlated to the difference of mass and the possibility of nuclear collisions.