Ya. Ya. Kudryk

Au-TiBx-n-6H-SiC Schottky barrier diodes: Specific features of charge transport in rectifying and nonrectifying contacts

Mechanism of charge transport in a diode of a silicon carbide’s Schottky barrier formed by a quasi-amorphous interstitial phase TiBx on the surface of n-6H-SiC (0001) single crystals with an uncompensated donor (nitrogen) concentration of ∼1018 cm−3 and dislocation density of ∼(106–108) cm−2 has been studied. It is demonstrated that, at temperatures T ≲ 400 K, the charge transport is governed by the tunneling current along dislocations intersecting the space charge region. At T > 400 K, the mechanism of charge transport changes to a thermionic mechanism with a barrier height of ∼0.64 eV and ideality factor close to 1.3.

Effect of p-n junction overheating on degradation of silicon high-power pulsed IMPATT diodes

The thermal limits of the two-drift impact avalanche and transit-time (IMPATT) diode operating in the pulsed mode in the 8-mm wavelength region with a microwave power as high as 30–35 W have been estimated. It is shown that p-n junction overheat at an operating pulse length of 300 ns and a supply current amplitude of 11.3–15 A amounts to 270–430°C relative to an ambient medium. The temperature limit of junction overheating, above which IMPATT diodes rapidly degrade, was determined as 350°C. The presented results of X-ray phase analysis and depth profiles of Au-Pt-Ti-Pd-Si ohmic contact components confirm thermal limits of the IMPATT diode operating in the pulsed mode.

The mechanism of contact-resistance formation on lapped n-Si surfaces

Anomalous temperature dependences of the specific contact resistance ρc(T) of Pd2Si-Ti-Au ohmic contacts to lapped n-Si with dopant concentrations of 5 × 1016, 3 × 1017, and 8 × 1017 cm−3 have been obtained. The anomalous dependences of ρc(T) have been accounted for under the assumption that the current flows along nanodimensional metallic shunts, which are combined with dislocations with a diffusionrelated limit in the supply of charge carriers taken into account. The densities of conducting and scattering dislocations in the surface region of the semiconductor are determined.

Temperature dependence of contact resistance for Au-Ti-Pd2Si-n+-Si ohmic contacts subjected to microwave irradiation

Based on a theoretical analysis of the temperature dependence of the contact resistance Rc for an Au-Ti-Pd2Si-n+-Si ohmic contact, a current-transfer mechanism explaining the experimentally observed increase in Rc in the temperature range 100–380 K is proposed. It is shown that microwave treatment of such contacts results in a decrease in the spread of Rc over the wafer and a decrease in the value of Rc whilst retaining an increase in Rc in the temperatures range 100–380 K.

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 ρc of ohmic contacts to n-n+-n++-GaAs(GaP, GaN, InP) structures with increasing measurement temperature T, experimentally observed in the temperature range 100–400 K, is suggested on the basis of a theoretical analysis of the temperature dependence of ρc. Good agreement between the experimental and theoretical ρc(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.

Thermal-resistant TiB x -n-GaP Schottky diodes

The effect of rapid thermal annealing on the parameters of TiBx-n-GaP Schottky barriers and interphase interactions at the TiBx-GaP interface are studied. It is shown that the contact TiBx-n-GaP system features an increased thermal stability without varying the electrical parameters of the Schottky barrier at temperatures as high as 600°C.

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-TiBx-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 ρc 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-TiBx-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.

The effect of current crowding on the internal quantum efficiency of InAsSb/InAs light-emitting diodes

The effect of current crowding on the internal quantum efficiency (IQE) of InAsSb/InAs light-emitting diodes (LEDs) operating in the middle-infrared (mid-IR) range (λ = 3−5 μm) has been studied. Calculations based on a modified model of recombination coefficients show that current crowding leads to a significant decrease in the IQE of LEDs, which is especially pronounced in longer-wavelength devices (23% at λ = 3.4 μm versus 39% at λ = 4.2 μm). The obtained results indicate that the effect of current crowding should be taken into consideration as an additional nonthermal mechanism of IQE decrease in mid-IR LEDs.

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.

Formation mechanism of contact resistance to III–N heterostructures with a high dislocation density

The temperature dependences of the contact resistance ρc(T) of ohmic Pd-Ti-Pd-Au contacts to n-GaN and n-AlN wide-gap semiconductors with a high dislocation density are studied. The dependences ρc(T) for both contacts contain portions of exponential decrease ρc(T) and very weak dependence ρc(T) at higher temperatures. Furthermore, a plateau portion ρc(T) is observed in the low-temperature region for the Au-Pd-Ti-Pd-n-GaN contact. This portion appears only after rapid thermal annealing (RTA). In principle, the appearance of the plateau portion can be associated with preliminary heavy doping of the near-contact region with a shallow donor impurity and with doping during contact fabrication as a result of RTA, if the contact-forming layer contains a material that is a shallow donor in III–N. The dependences obtained are not explained by existing charge-transport mechanisms. Probable mechanisms explaining the experimental dependences ρc(T) for ohmic contacts to n-GaN and n-AlN are proposed.