Radiation effects and interphase interactions in ohmic and barrier contacts to indium phosphide as induced by rapid thermal annealing and irradiation with γ-ray 60Co photons

The radiation resistance of Au-Pd-Ti-Pd-n ⁺⁺-InP ohmic contacts and Au-TiB _x -n-n ⁺-n ⁺⁺-InP barrier contacts—both initial and subjected to a rapid thermal annealing and irradiated with ⁶⁰Co γ-ray photons with doses as high as 10⁹ R—has been studied. Before and after external effects, the electrical characteristics of the barrier and ohmic contacts, distribution profiles for components, and phase composition in the metallization layers have been measured. In ohmic Pd-Ti-Pd-Au contacts subjected to rapid thermal annealing and irradiation, a significant distortion of the layered structure of metallization occurs; this distortion is caused by the thermal and irradiation-stimulated transport of Pd over the grain boundaries in polycrystalline Ti and Au films. However, the specific contact resistance ρ _c does not change appreciably, which is related to a comparatively unvaried composition of the contact-forming layer at the Pd-n ⁺-InP interface. In the initial sample and the sample subjected to the rapid thermal annealing at T = 400°C with the Au-TiB _x -n-n ⁺-n ⁺⁺-InP barrier contacts and irradiated with the dose as high as 2 × 10⁸ R, a layered structure of metallization is retained. After irradiation with the dose as high as 10⁹ R, in the samples subjected to a rapid thermal annealing at T = 400°C, the layered structure of metallization becomes completely distorted; however, this structure is retained in the initial sample. The electrical properties of the contact structure appreciably degrade only after irradiation of the sample preliminarily subjected to a rapid thermal annealing at T = 400°C.     

Effect of microwave irradiation on the resistance of Au-TiB x -Ge-Au-n-n +-n ++-GaAs(InP) ohmic contacts

Temperature dependences of the contact resistivity ρ _c of Au-TiB _x -Ge-Au-n-n ⁺-n ⁺⁺(GaAs)-InP ohmic contacts before and after short-term (10 s) microwave treatment have been studied both experimentally and theoretically. It is shown that ρ _c can decrease after microwave treatment in the entire temperature range of ρ _c measurements (100–400 K). Good agreement between the theoretical and experimental ρ _c (T) curves is attained and interpreted on the assumption that the dislocation density in the semiconductor near-surface region is varied as a result of microwave radiation.     

Effective recombination velocity at the NN+ interface

The effective recombination velocity S_nn⁺ at the nn⁺ interface in buried layer (nn⁺p) and n epi-n⁺ substrate structures has been studied using a model which takes into account the retarding outdiffusion region, recombination and bandgap narrowing. The variation of S_nn⁺ with diffusion length and bandgap narrowing has been estimated taking into consideration their doping-dependence. An attempt has been made to explain the wide range in the reported values for S_nn⁺ using the results of this study.Results indicate clearly the difference between the S_nn⁺ of the two structures. This difference arises from the collection by the p-substrate which accounts for a significant part of the S_nn⁺ of the buried layer structure over a wide range of values of diffusion length. This collection component of S_nn⁺ is sensitive to bandgap narrowing.On the other hand, the S_nn⁺ of the nn⁺ structure is largely determined by the recombination in the outdiffusion region which is sensitive mainly to the value of diffusion length in that region. The component of S_nn⁺ representing recombination in the n⁺ substrate is sensitive to bandgap narrowing. The present study indicates the dependence of S_nn⁺ on the structure and processing of the devices in which the nn⁺ interface occurs.     

Optimization of the deposition and annealing conditions of fluorine-doped indium oxide films for silicon solar cells

Fluorine-doped indium oxide (IFO) films are deposited onto (pp ⁺)Si and (n ⁺ nn ⁺)Si structures made of single-crystal silicon by ultrasonic spray pyrolysis. The effect of the IFO deposition time and annealing time in an argon atmosphere with methanol vapor on the IFO chemical composition, the photovoltage and fill factor of the Illumination-U _oc curves of IFO/(pp ⁺)Si structures, and the sheet resistance of IFO/(n ⁺ nn ⁺)Si structures, correlating with the IFO/(n ⁺)Si contact resistance, is studied. The obtained features are explained by modification of the properties of the SiO _x transition layer at the IFO/Si interface during deposition and annealing. Analysis of the results made it possible to optimize the fabrication conditions of solar cells based on IFO/(pp ⁺)Si heterostructures and to increase their efficiency from 17% to a record 17.8%.     

Analysis of characteristics of photodetectors based on InGaAs heteroepitaxial structures for 3D imaging

The 320 × 256 focal plane arrays based on р ⁺ -B–n-N ⁺ tetralayer heterostructures with a wide-gap barrier layer have been investigated. The heterostructures with a narrow-gap n-InGaAs absorbing layer were grown by means of metalorganic vapor phase epitaxy on InP substrates. The band discontinuity between the In_0.53Ga_0.47As absorbing layer and the In_0.52Al_0.48As barrier layer is removed by growing a thin four-component n-AlInGaAs layer with the bandgap gradient variation. Delta-doped layers included into the heterostructures make it possible to lower the barrier in the valence band and eliminate the nonmonotonicity of energy levels. The experimental study of the dark current has been performed. It has been revealed that the average value of the dark current does not exceed 10 fA for the photodiode arrays with a pitch of 30 μm.     

Influence of Annealing on Electrical Properties of an Organic Thin Layer-Based n-Type InP Schottky Barrier Diode

The electrical properties of a fabricated Au/polymethylmethacrylate (PMMA)/n-InP Schottky barrier diode have been analyzed for different annealing temperatures using current–voltage (I–V) and capacitance–voltage (C–V) techniques. It is observed that the Au/PMMA/n-InP structure shows excellent rectifying behavior. The extracted barrier height and ideality factor of the as-deposited Au/PMMA/n-InP Schottky contact are 0.68 eV (J–V)/0.82 eV (C–V) and 1.57, respectively. However, the barrier height (BH) of the Au/PMMA/n-InP Schottky contact increases to 0.78 eV (J–V)/0.99 eV (C–V) when the contact is annealed at 150°C for 1 min in nitrogen atmosphere. Upon annealing at 200°C, the BH value decreases to 0.72 eV (J–V)/0.90 eV (C–V) and the ideality factor increases to 1.48. The PMMA layer increases the effective barrier height of the structure by creating a physical barrier between the Au metal and the n-InP. Cheung’s functions are also used to calculate the series resistance of the Au/PMMA/n-InP structure. The interface state density (N _ss) is found to be 6.380 × 10¹² cm^?2 eV^?1 and 1.916 × 10¹² cm^?2 eV^?1 for the as-deposited and 150°C-annealed Au/PMMA/n-InP Schottky contacts, respectively. These results indicate that the interface state density and series resistance have a significant effect on the electrical characteristics of Au/PMMA/n-InP Schottky barrier devices. Finally, it is noted that the diode parameters change with increasing annealing temperature.     

Injection currents in silicon structures with blocked hopping conduction

It is shown that injection currents in structures with blocked hopping conduction (the so-called BIB structures) may be interpreted as Richardson thermionic currents flowing through potential barriers. The latter are governed by the electron chemical potential in the N ⁺⁺-N ⁺ (N ⁺⁺-I) regions. It is also shown that measurement of the injection potential is a convenient method for determining the degree of compensation in silicon structures with “ohmic” contacts.     

Electron thermal emission rates of nickel centers in silicon

The majority carrier thermal emission rates of nickel levels in the depletion region of reverse biased silicon p⁺ nn⁺ junctions have been investigated using the admittance spectroscopy technique. We have found two levels associated with nickel in n-type silicon. The “thermal activation energies” have values of E_C − 360 ± 10 meV and E_C − 570 ± 10 meV.     

Theoretical Modeling of HOT HgCdTe Barrier Detectors for the Mid-Wave Infrared Range

This paper reports on theoretical modeling of medium-wavelength infrared HgCdTe barrier infrared detector (BIRD) photoelectrical performance. BIRD HgCdTe detectors were simulated with the commercially available software APSYS. Detailed analysis of the detector performance such as dark current, photocurrent, resistance–area product, detectivity versus applied bias, operating temperature, and structural parameters (absorber doping, barrier composition) was performed to determine the optimal operating conditions. It is shown that higher operation temperature conditions achievable with commonly used thermoelectric coolers allow detectivities of D = 9.5 × 10¹⁰ cmHz^1/2/W and D ^* = 1.5 × 10¹¹ cmHz^1/2/W at T = 200 K to be obtained for the correct absorber doping for nB_nnn⁺ and nB_npn⁺, respectively. R ₀ A for the nB_nnn⁺ detector was found to range from 200 Ω cm² to 0.6 Ω cm² at T = 200 K to 300 K, respectively.     

Finite metal-sheet-resistance in contact resistivity measurements: Application to Si/TiN contacts

The standard transmission line model cannot be applied to evaluate the contact resistivity of thin TiN layers on highly doped p⁺ and n⁺ substrates because the finite sheet resistance of the TiN must be accounted for. We present two ways to include this effect using existing analytical models. The results are shown to agree with measurements where the effect of the finite sheet resistance of TiN is eliminated with a metallic overlayer. With the help of these evaluation techniques, it is shown that the contact resistivity of TiN changes in opposite ways for p⁺ and n⁺Si after vacuum annealing at 600°C for 15 min. This result is consistent with an increase of the barrier height φ_Bn of the contact by ?0.1 V to near midgap value.     

Study of the potential distribution in a forward-biased silicon diode using electrostatic force microscopy

Electrostatic force microscopy was used to study the potential distribution in a forward-biased epitaxial-diffused n ⁺-n-p-p ⁺ silicon diode. Distributions of potential and capacitance were determined across the cleaved surface, which intersected the layers in the diode structure. Variations in the surface potential and capacitance were preliminarily measured with a submicrometer spatial resolution and were used to determine the position and width of the n-p junction; the distribution of applied forward bias in the diode was also assessed. It is shown that an additional potential barrier for injected charge carriers may exist in the vicinity of the n ⁺-n junction in the diode under consideration. For an injection-current density exceeding 100 mA/cm², the voltage drop across this barrier becomes comparable with the voltage variations across the operating n-p junction.     

Novel Diffusion‐Barrier Materials Against Oxygen for High‐Density Dynamic Random Access Memory Capacitors

A new design concept for diffusion barriers in high‐density memory capacitors is suggested, and both RuTiN (RTN) and RuTiO (RTO) films are proposed as sacrificial oxygen diffusion barriers. The newly developed RTN and RTO barriers show a much lower sheet resistance than various other barriers, including binary and ternary nitrides (reported by others), up to 800 °C, without a large increase in the resistance. For both the Pt/RTN/TiSi_x/n⁺⁺poly‐plug/n⁺ channel layer/Si and the Pt/RTO/RTN/TiSi_x/n⁺⁺poly‐plug/n⁺ channel layer/Si contact structures, contact resistance—the most important electrical parameter for the diffusion barrier in the bottom electrode structure of capacitors—was found to be as low as 5 kohm, even after annealing up to 750 °C. When the RTN film was inserted as a glue layer between the bottom Pt electrode layer and the TiN barrier film in the chemical vapor deposited (Ba,Sr)TiO₃ (CVD–BST) simple stack‐type structure, the RTN glue layer was observed to be thermally stable to temperatures 150 °C higher than that to which the TiN glue layer is stable. Moreover, the capacitance of the physical vapor deposited (PVD)–BST simple stack‐type structure adopted TiN glue layer initially degraded after annealing at 500 °C, and, thereafter, completely failed. In the case of the RTN and RTO/RTN glue layers, however, the capacitance continuously increased up to 550 °C. Thus, the new RTN and RTO films, which act as diffusion barriers to oxygen, are very promising materials for achieving high‐density capacitors.     

Avalanche Mechanism in p +-n −-n + and p +-n Mid-Wavelength Infrared Hg1−x Cd x Te Diodes on Si Substrates

Hg_1−x Cd _x Te mid-wavelength infrared (MWIR) p ⁺-n ⁻-n ⁺ and p ⁺-n ⁻ avalanche photodiodes (APDs) with a cut-off of 4.9 μm at 80 K were fabricated on Si substrates. Diode characteristics, avalanche characteristics, and excess noise characteristics were measured on two devices. Temperature-dependent diode and avalanche characterization was performed. Maximum 3 × 10⁶ Ω cm² and 9 × 10⁵ Ω cm² zero-bias resistance times active area (R ₀ A) products were measured for the p ⁺-n ⁻-n and p ⁺-n devices at 77 K, respectively. Multiplication gains of 1250 and 410 were measured at −10 and −4 V for the p ⁺-n ⁻-n ⁺ and p ⁺-n APDs at 77 K, respectively, in the front-illumination mode with the help of a laser with an incident wavelength of 632 nm. The gains reduce to 200 and 50 at 120 K, respectively. The excess noise factor in all APDs was measured to be in the range of 1 to 1.2.     

CdHgTe heterostructures for new-generation IR photodetectors operating at elevated temperatures

The parameters of multilayer Cd_xHg_1–xTe heterostructures for photodetectors operating at wavelengths of up to 5 μm, grown by molecular-beam epitaxy (MBE) on silicon substrates, are studied. The passivating properties of thin CdTe layers on the surface of these structures are analyzed by measuring the C–V characteristics. The temperature dependences of the minority carrier lifetime in the photoabsorption layer after growth and thermal annealing are investigated. Samples of p ⁺–n-type photodiodes are fabricated by the implantation of arsenic ions into n-type layers, doped with In to a concentration of (1–5) × 10¹⁵ cm^–3. The temperature dependences of the reverse currents are measured at several bias voltages; these currents turn out to be almost two orders of magnitude lower than those for n ⁺–p-type diodes.     

Comparative investigation of InP/InGaAs heterostructure-emitter tunneling and superlattice bipolar transistors

In this article, the characteristics of InP/InGaAs heterostructure-emitter bipolar transistors with 30 n-InP layer tunneling layers and a five-period InP/InGaAs superlattice are demonstrated and comparatively investigated by experimentally results and analysis. In the three devices, a 200 Å n-In_0.53Ga_0.47As layer together with an n-InP tunneling emitter layer (or n-InP/n-InGaAs superlattice) forms heterostructure emitter to decrease collector-emitter offset voltage. The results exhibits that the largest collector current and current gain are obtained for the tunneling transistor with a 30 Å n-InP tunneling emitter layer. On the other hand, some of holes injecting from base to emitter will be blocked at n-InP/n-InGaAs heterojunction due to the relatively small hole transmission coefficient in superlattice device, which will result in a considerable base recombination current in the n-InGaAs layer. Therefore, the collector current and current gain of the superlattice device are the smallest values among of the devices.     

Unterminated 4H-SiC Schottky barrier diodes with novel HfNxBy electrodes

4H-SiC Schottky barrier diodes (SBDs) were fabricated and characterized from room temperature to 573 K using HfN_xB_y as Schottky electrodes. The results are compared to SBDs fabricated using other electrodes that include Ni, Pt, Ti and Au. The Schottky barrier height Φ_b for as-deposited HfN_xB_y/n−/n+ diodes, determined from room temperature current-voltage characteristics, is 0.887 eV. This is lower than those of SBDs fabricated using other metals such as Au, where Φ_b is 1.79 eV. The HfN_xB_y/n−/n+ diodes studied have a much higher on-resistance R_on of around 38.24 mΩ-cm², which is about four times that of Au/n−/n+ diodes, due to the higher sheet resistance of the sputtered HfN_xB_y electrode layer. The barrier height Φ_b and ideality factor η of the HfN_xB_y/n−/n+ diodes remain almost unchanged after 400 and 750 °C anneal in N₂. This suggests excellent thermal and chemical stability of HfN_xB_y in contact with 4H-SiC.     

High-efficiency dual-junction GaInP/GaAs tandem solar cells obtained by the method of MOCVD

Monolithic dual-junction GaInP/GaAs solar cells grown by the MOCVD method were studied. The conditions of the growth of ternary Ga _x In_1?x P and Al _x In_1?x P alloys lattice-matched to GaAs are optimized. Technology for fabrication of a tunneling diode with a high peak current density of 207 A/cm² on the basis of heavily doped n ⁺⁺-GaAs:Si and p ⁺⁺-AlGaAs:C layers is developed. Cascade GaInP/GaAs solar cells obtained as a result of relevant studies featuring a good efficiency of the solar-energy conversion both for space and terrestrial applications. The maximum value of the GaInP/GaAs solar-cell efficiency was 30.03% (at AM1.5D, 40 suns).     

Temperature dependence of the contact resistance of ohmic contacts to III–V compounds with a high dislocation density

A new mechanism describing the rise in the contact resistance ?? _c of ohmic contacts to n-n ⁺-n ⁺⁺-GaAs(GaP, GaN, InP) structures with increasing measurement temperature T, experimentally observed in the temperature range 100?C400 K, is suggested on the basis of a theoretical analysis of the temperature dependence of ?? _c . Good agreement between the experimental and theoretical ?? _c (T) dependences is obtained and explained for a case where there is a high density of dislocations (on which metallic shunts are localized) in the near-contact region of the semiconductor.     

Electrical characteristics of laser-contacted diodes

We have fabricated p⁺-n and Schottky diodes with contacts made of laser-formed palladium-silicide. The electrical characteristics of these diodes are presented. The reverse currents and breakdown voltages are comparable to conventionally contacted p⁺-n diodes. The barrier height of laser-formed Schottky diodes agrees well with published values for Pd₂Si. The promising results point out the potential applications of contact formation by laser irradiation in device manufacture.     

Influence of the variband-layer thickness on the energy and frequency characteristics of In x(z)Ga1 − x(z)As Gunn diodes

The operation of variband-In _x(z)Ga_{1 − x(z)}As Gunn diodes with an active-region length of 2.5 μm and an n ⁺-n cathode contact is studied by using a two-temperature model of electron intervalley transfer in a varib-and semiconductor. It is established that, in diodes, dipole domains or accumulation layers may be formed depending on the variband-layer thickness. The use of variband In _x(z)Ga_{1 − x(z)}As in the active region with an appropriate variband-layer thickness allows one to enhance the output power and the generation efficiency by a factor of approximately 1.5 and to increase the width of the frequency range of the diode operation approximately twofold as compared to that of an In_0.2Ga_0.8As-based diode. Original Russian Text ? Yu.V. Arkusha, E.D. Prokhorov, I.P. Storozhenko, 2006, published in Radiotekhnika i Elektronika, 2006, Vol. 51, No. 3, pp. 371–378.