Yu. N. Sveshnikov

Schottky contacts to high-resistivity epitaxial GaAs layers for detectors of particles and X- or γ-ray photons

The electrical characteristics of Ti and Pt Schottky contacts to epitaxial n-GaAs layers with the charge-carrier concentration <1012 cm−3 for detectors of particles and X- or γ-ray photons are studied. It is shown that it is preferable to use a diffusion-based theory of charge transport in calculations of the parameters of Schottky contacts to thick high-resistivity lightly compensated GaAs layers. The calculated barrier heights were 0.84 and 0.87 eV for the Ti and Pt contacts, respectively. The fabricated samples of the surface-barrier detectors featured a linear response in the studied range of energies from 6 to 140 keV for γ-ray photons and from 4 to 8 MeV for α particles; the efficiency of charge collection was close to 100% and the energy resolution was high at room temperature.

Study of the Electron Distribution in GaN and GaAs after γ-Neutron Irradiation

The results of experimental studies of the parameters of GaN and GaAs structures before and after γ-neutron irradiation are reported. A special set of test diodes making it possible to reduce the error in the results of measuring the parameters of the structures, which is important in the design and optimization of the structure of semiconductor devices, is suggested.

Effect of microwave treatment on current flow mechanisms in Au-TiBx-Al-Ti-n+-n-n+-GaN-Al2O3 ohmic contacts

The temperature dependences of the contact resistivity ρc of Au-TiBx Al-Ti-n+-n-n+-GaN-Al2O3 ohmic contacts have been studied before and after microwave treatment followed by nine-nonth room-temperature sample storage. The temperature dependences of ρc of initial samples were measured twice. The first measurement showed the temperature dependence typical of ohmic contacts; the repeated measurement in the temperature region above 270 K showed a ρc increase caused by metallic conductivity. After microwave treatment, the metallic conductivity in the ohmic contact is not observed. This is presumably associated with local heating of metal Ga inclusions under microwave irradiation and the formation, due to high chemical activity of liquid gallium, of compounds of it with other metallization components. In this case, the temperature dependence of ρc is controlled by ordinary charge transport mechanisms. After nine-nonth room-temperature storage, the temperature dependence of ?c is described by the tunneling mechanism of charge transport.

Mechanism of current flow in a Au-Ti-Al-Ti-n+-GaN ohmic contact in the temperature range of 4.2–300 K

The temperature dependence of the contact resistivity ρc(T) of Au-Ti-Al-Ti-n+-GaN ohmic contacts is studied experimentally and substantiated theoretically in the temperature range T = 4.2–300 K. It is shown that the saturation portion of ρc(T) is observed in the low-temperature measurement region (4.2–50 K). As the temperature increases, ρc decreases by the exponential law. The experimental and calculated dependences ρc(T) are in agreement. The obtained results make it possible to conclude the field nature of the current transfer for the saturation region of ρc(T) and the thermal-field one, for the exponential region.

Radiation damage of contact structures with diffusion barriers exposed to irradiation with 60Coγ-ray photons

The effect of ionizing radiation of 60Co γ-ray photons in the dose range 104–2 × 109 rad on metal-semiconductor Au-ZrBx-AlGaN/GaN and Au-TiBx-Al-Ti-n-GaN contacts and Au-ZrBx-n-GaN Schottky diodes is examined. The contacts with the TiBx and ZrBx diffusion barriers do not degrade under the effect of ionizing radiation if the dose does not exceed 108 rad. The Au-ZrBx-n-GaN Schottky diodes remain stable in the dose range 104–106 rad. As the radiation dose is increased to ≳108 rad, the damage to the contact metallization increases and is accompanied by formation of through pores, which is conducive to accumulation of oxygen at the Au-ZrBx(TiBx) interfaces and to an increase in mass transport of atoms in contact-forming layers. In this case, irradiation-caused degradation of the Schottky diodes is observed. Possible mechanisms of radiation damage of contact structures with diffusion barriers are analyzed.

Thermal stability of multilayer contacts on gallium nitride

The results of investigation of a new system of metallization for nonrectifying contacts on n-GaN are presented. The new contact metallization system involves the following sequence of layers: Au(200 nm)-Ti(TiBx)(100 nm)-Al(20 nm)-Ti(50 nm), where the TiBx layer plays the role of a diffusion barrier. The contacts with the TiBx layer retain their layer structure and electrical characteristics upon annealing up to 700°C, whereas the usual Au-Ti-Al-Ti structure exhibits degradation upon rapid thermal annealing at T = 700°C. Further increase in the annealing temperature to 900°C leads to smearing of the layer structure of the Au-TiBx-Al-Ti-GaN contact. Physical factors responsible for the change in the parameters of such contact systems are considered.

Radiation effects in multilayer ohmic contacts Au-Ti-Al-Ti-n-GaN

Radiation effects in the Au-Ti-Al-Ti-n-GaN multilayer metallization subjected to irradiation with 60Co γ-ray photons in the dose range 4 × 106−2 × 107 Gy are considered, and the effect of radiation on the initial contact structures and the structures subjected to a rapid thermal annealing (RTA) at high-temperature in the nitrogen atmosphere is studied. Irradiation does not significantly affect the properties of structures that were not subjected to the heat treatment. An RTA at 700°C brings about a deterioration of the contact-layer morphology. The morphological and structural transformations in the contact metallization due to the RTA are enhanced by irradiation with γ-ray photons. The combined radiation-thermal treatment is conducive to the mass transfer between contacting layers. In addition, after γ-ray irradiation with the dose of 2 × 107 Gy, the oxygen-impurity atoms appear over the entire contact’s structure and are observed in a large amount in the near-contact GaN region.

Nitride gallium high power integrated heterostructure FETs

The heterostructures AlGaN/AlN/GaN, grown on sapphire substrates, the standard design of the integrated power HFET and the design with the additional field-plate, and its technology have been developed. The HFETs have given output power 4,5-5,5 and 3-4 W/mm, and power gain 4,5-7,5 N 3,8-6,0 dB at frequencies 12 and 17,5 GHz.

On the Current Flow Mechanism in Au-TiB x -n-GaN-i-Al 2 O 3 Schottky Barrier Diodes

We investigated a current flow mechanism in the Au-TiBx-n-GaN-i-AI2O3 Schottky barrier diodes, in which space-charge region width is much over the de Broglie wavelength in GaN. An analysis of the temperature dependences of l-V curves of forward-biased Schottky barriers showed that, in the 80-380 K temperature range, current flow occurs as tunneling along dislocations crossing the space-charge region. The dislocation density p estimated from l-V curves (in accordance with the model of tunneling along the dislocation line) was ap 1.7 times 10-7 cm-2.

Heat-Resistant Au-TiBx-n-GaN Schottky Diodes

We studied phase composition and parameters of the ohmic Au-TiB x-Al-Ti-n-GaN and barrier Au-TiBx-n-GaN contacts, both before and after rapid thermal annealing (RTA) at T=870degC for 30 s. The phase composition was studied with X-ray diffraction technique, while the parameters of the ohmic contacts were studied for the transmission line method (TLM) structures and those of the barrier contacts were studied by measuring the forward branches of I-V curves with further calculation of the Schottky barrier (SB) height phiB and ideality factor n. It was found that low-resistance (rhocap(1divide3)times10-6 Omegamiddotcm2 ohmic Au-TiBx-Al-Ti-n-GaN contacts can be formed using RTA. It turned out also that, after RTA at T=870degC for 30s, the SB retains its barrier properties practically unchanged, as compared with the initial sample that has not been exposed to RTA