V. V. Emtsev

Absorption and Emission of Hexagonal InN. Evidence of Narrow Fundamental Band Gap

(a) Ioffe Physico-Technical Institute, Russian Academy of Science, Polytekhnicheskaya 26, 194021 St. Petersburg, Russia (b) Institut für Festkörpertheorie and Theoretische Optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany (c) Department of Electronics and Information Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan (d) Institute of Solid State and Semiconductor Physics, Belarus Academy of Sciences, Brovki 17, 220072 Minsk, Belarus (e) LfI, University of Hannover, Schneiderberg 32, D-30167 Hannover, Germany

Band Gap of Hexagonal InN and InGaN Alloys

A survey of most recent studies of optical absorption, photoluminescence, photoluminescence excitation, and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented. The samples studied were undoped n-type InN with electron concentrations between 6 × 10 18 and 4 × 10 19 cm -3 . It has been found that hexagonal InN is a narrow-gap semiconductor with a band gap of about 0.7 eV, which is much lower than the band gap cited in the literature. We also describe optical investigations of In-rich In x Ga 1-x N alloy layers (0.36 < x < 1) which have shown that the bowing parameter of b ∼ 2.5 eV allows one to reconcile our results and the literature data for the band gap of In x Ga 1-x N alloys over the entire composition region. Special attention is paid to the effects of post-growth treatment of InN crystals. It is shown that annealing in vacuum leads to a decrease in electron concentration and considerable homogenization of the optical characteristics of InN samples. At the same time, annealing in an oxygen atmosphere leads to formation of optically transparent alloys of InN-In 2 O 3 type, the band gap of which reaches approximately 2 eV at an oxygen concentration of about 20%. It is evident from photoluminescence spectra that the samples saturated partially by oxygen still contain fragments of InN of mesoscopic size.

Experimental and theoretical studies of phonons in hexagonal InN

The first- and second-order Raman scattering and IR reflection have been studied for hexagonal InN layers grown on (0001) and (1102) sapphire substrates. All six Raman-active optical phonons were observed and assigned: E2(low) at 87 cm−1, E2(high) at 488 cm−1, A1(TO) at 447 cm−1, E1(TO) at 476 cm−1, A1(LO) at 586 cm−1, and E1(LO) at 593 cm−1. The ratio between the InN static dielectric constants for the ordinary and extraordinary directions was found to be e⊥0/e∥0=0.91. The phonon dispersion curves, phonon density-of-state function, and lattice specific heat were calculated. The Debye temperature at 0 K for hexagonal InN was estimated to be 370 K.

Electronic properties of antimony-vacancy complex in Ge crystals

Schottky barriers formed by depositing Au on n-type Ge have been used to study the antimony-vacancy complex (E center). Both hole and electron transitions have been observed because the formation of an inversion layer at the semiconductor surface enables minority carriers to be injected when the Schottky barrier is forward biased. It is argued that the E center in Ge has three charge states: double negative, single negative, and neutral. The free energy of electron ionization for the double acceptor level of the complex has been found to be ΔG(=/−)=0.294−4.2 kT (eV), where k is Boltzmann’s constant. Consequently, the position of the double acceptor level of the E center {E(=/−)=Ec−ΔG(=/−)} is temperature dependent. In moderately Sb-doped (NSb=1013–1015 cm−3) Ge crystals at equilibrium conditions half-occupancy of the double acceptor state of the Sb-V complex occurs when the Fermi level is at about Ec−0.20 eV. The single acceptor level of the E center is in the lower part of the band gap. The activation en...

Radiation-induced defects in Czochralski-grown silicon containing carbon and germanium

Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (CiOi) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [Cs] up to 1 × 1017 cm−3 and Ge concentrations [Ge] up to 1 × 1020 cm−3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [Cs] around 2 × 1017 cm−3 the production rate of VO defects is getting larger by ~40% in Cz–Si:Ge at Ge concentrations around 1 × 1019 cm−3 and then at [Ge] ≈ 2 × 1020 cm−3 this enlargement drops to ~13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of CiOi complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm−1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes.

Mg‐Doped Hexagonal InN/Al2O3 Films Grown by MBE

We report on the first attempts of Mg doping of hexagonal InN/Al2O3(0001) films grown by plasma-assisted molecular beam epitaxy. A dramatic improvement of crystalline quality of InN : Mg epilayers has been observed at the magnesium concentration in the 1019 to 3 ×1020 cm—3 range as indicated by triple-crystal X-ray diffraction θ-rocking curve peak width below 30 arcsec. An increase of Mg doping higher than 1021 cm—3 deteriorates dramatically the InN crystal quality and surface morphology. A thermodynamic model of the surfactant Mg effect is proposed. The increase in Mg concentration causes the reduction by an order of magnitude (down to n = 1019 cm—3) of free electron concentration in InN : Mg layers compared to undoped ones, accompanied by a significant reduction of electron mobility. This behavior can be explained by a complex effect of the crystal quality improvement and the carrier compensation by incorporated Mg acceptors.

Radiation effects on the behavior of carbon and oxygen impurities and the role of Ge in Czochralski grown Si upon annealing

The annealing behavior of the oxygen and carbon impurities in Czochralski grown silicon (Cz-Si) was investigated in electron- and neutron-irradiated materials. The irradiated samples were subjected to isochronal anneals of up to ∼1000 °C, and the evolution of oxygen and carbon concentrations was monitored by means of infrared spectroscopy from the amplitudes of the 1106 and 605 cm−1 bands of the two impurities correspondingly. It was found that the electron irradiation does not affect the temperature of annealing of oxygen, although in the neutron-irradiated samples the oxygen band begins to decay in the spectra at a lower temperature than that in the nonirradiated samples. This behavior could be determined by supersaturation of vacancies mainly liberated from disordered regions in the latter material. This assists the oxygen aggregation process. Regarding carbon evolution, it was found that in the irradiated samples the annealing out of the 605 cm−1 band occurs at a lower temperature than that of the non...

Point defects in gamma-irradiated n-GaN

Radiation-induced point defects and their annealing in silicon-doped n-GaN have been investigated by means of Hall effect measurements and Raman spectroscopy. Correlated compensation effects due to simultaneous introduction of donor and acceptor centres are observed in irradiated n-GaN. The defect production rate is dependent on the dopant concentration. This means that the model of all native defects immobile at room temperature is not true. The behaviour of radiation-induced defects upon heating is complicated, exhibiting two prominent stages of reverse annealing. The presence of radiation defects is still observable after annealing to T = 750 °C.

Oxygen aggregation in Czochralski-grown silicon heat treated at 450 °C under compressive stress

It has been established that the oxygen aggregation processes in Czochralski-grown silicon (Cz–Si) at 450 °C are strongly affected by high hydrostatic pressure. We observed the enhanced production of shallow thermal donors with ionization energies of 30–40 meV and deep donors at ≈EC−0.1 eV under a pressure of 1 GPa. In contrast, the concentration of the well-known double thermal donors was found to be much less than that in Cz–Si heat treated without stress. The latter effect may be associated with the involvement of self-interstitials in their formation. The enhanced production of other thermal donors is thought to be caused by increasing diffusivity of oxygen under the high stress.

IR studies of the impact of Ge doping on the successive conversion of VOn defects in Czochralski-Si containing carbon

We report infrared absorption studies of oxygen-related defects in electron-irradiated Ge-doped Czochralski-Si. Our investigation was mainly focused on the reaction channel leading to the formation of VOn (1≤n≤6) defects. The VOn defects form mainly upon annealing, as a result of the successive aggregation of oxygen atoms in the initial VO defect produced by the irradiation: (VO+Oi→VO2+Oi→VO3+Oi→VO4,…). It was found that the ratio of the conversion of VOn to VOn+1 defects is sensitive to the Ge content of the material. In particular, the ratio of the conversion of the VO to the VO2 defects was found to decrease with the increase in Ge concentration of the samples, although the opposite trend was observed for the VO3 to VO4 conversion. However, the VO2 to VO3 conversion changes only slightly with Ge content, being practically unaffected for Ge concentrations up to 2×1020 cm−3. In the case of VO2 formation, the phenomenon was attributed to the elastic strains induced in the lattice due to the Ge presence wh...