Sergey Novikov

Characterization of epiready n + -GaAs (100) surfaces by SPV-transient

Surface photovoltage (SPV) transient provides a non-destructive, contact-free method for characterization of semiconductor surfaces. Here we study SPV-transients of differently cleaned, heavily doped epiready GaAs wafers. After a rapid initial part the transient shows a very slow decay taking place in 100 - 1000 s time scale. Chemical NH4OH:H2O2:H2O cleaning and atomic hydrogen UHV cleaning are applied. SPV-transients are measured by Kelvin probe in normal atmospheric conditions. A large signal surface trapping model is developed which includes both majority and minority carrier processes and covers the whole light on, steady state, light off sequence. Model fitting allows band bending, energy and density of surface states as well as electron and hole capture cross-sections to be extracted. The results show that the traps are electronic states in thin oxide layer covering the samples. This conclusion is based on the finding that the capture cross-sections are very small, in the range 10-19 - 10-26 cm2, which calls tunneling for explanation. This indicates that after cleaning the oxide layer is rapidly re-grown in laboratory atmosphere in less than 30 min. Typical band bendings are 0.6 - 0.8 eV, trap energies are slightly above the mid-gap and the density of occupied trap states is around 5×1012 cm-2 at thermal equilibrium.

Fabrication of ultrathin silicon dioxide layers in room temperature by ultrahigh vacuum plasma oxidation

Abstract Plasma oxidation of silicon in room temperature and in an ultrahigh vacuum has been found to be a useful tool in producing very thin silicon dioxide layers. The maximum thickness that can be reached, however, is only 1–1.1 nm. As the needed layer thickness is usually from 2 to 5 nm, the process has to be performed in several oxidation cycles. Using this method, a good thickness control can be achieved and the resulting MOS structures have relatively low surface state densities and a high breakdown field.

Magnetotransport properties of a room temperature ferromagnet (Ga, Mn)N

Heavily Mn-doped GaN thin films were fabricated by using solid-state diffusion. The magnetic properties of the samples were determined by Hall effect measurements and by using a superconducting quantum interference device. The results show ferromagnetic behavior even above room temperature, the Curie temperature being 330 K. The samples were of n-type and the estimated electron concentration was /spl ap/1/spl times/10/sup 20/ cm/sup -3/. Due to the spin-disorder scattering, a negative magnetoresistance was observed and it was largest at Curie temperature. The measured sheet resistance versus temperature could also be explained by the spin disorder scattering model for ferromagnetic metals. From the measurement results, the value of the exchange interaction parameter between the electron spins and the magnetic moments of the Mn atoms was estimated to be about 1 eV. The material properties were studied also by using secondary ion mass spectroscopy and X-ray diffraction, which showed some segregation of Ga/sub x/Mn/sub y/.

On light-emitting mechanism in Si/SiO 2 superlattices grown by molecular beam deposition

Abstract We investigate the photoluminescence (PL) of Si/SiO 2 superlattices grown by molecular beam deposition (MBD). The PL intensity is found to depend on a regime of oxide growth. The most emitting samples are those with SiO 2 layers grown in O 2 /H 2 mixture and having Si layer thickness of 1.2–1.8 nm. Our results suggest that the source of PL is the radiative recombination of carriers trapped from Si quantum wells to defect centers in the oxide.

Magnetic GaAs resonant tunnelling diodes with a Mn-doped emitter

We have fabricated ferromagnetic resonant tunnelling diodes (FRTD’s) based on the AlAs/GaAs/AlAs quantum wells and the p-type Mn-doped GaAs emitter layers. At low temperatures a large magnetic field dependence of the tunnelling current appears in the magnetic RTD’s in rather low fields (B < 1T), which is not found in nonmagnetic RTD’s. The observed decrease of current in the case of the metallic ferromagnetic emitters is explained by a tunnelling anisotropic magnetoresistance effect.

Magnetotransport in Ferromagnetic (Ga, Mn)As and (Ga, Mn)N Pn-Diodes

GaAs and GaN pn-junctions are fabricated with Mn-doped ferromagnetic layers on top of nonmagnetic substrates. In the case of heavily doped (Ga,Mn)As/GaAs p++n++-junctions (Zener diodes) the tunneling current becomes magnetic field dependent at low temperatures. This can be explained by a model based on the valence band splitting due to the exchange interaction between the hole spins and the localized spins of the Mn atoms. In the pn-junctions with more lightly doped nonmagnetic regions in the (Ga, Mn)N and (Ga, Mn)As diodes, no magnetic field dependence in the I-V characteristics is observed, probably due the absence of ferromagnetism in the depletion region of the p+n-junctions

Strong yellow electroluminescence from manganese-silicon-implanted silicon-dioxide layers

Room temperature (RT) electroluminescence (EL) was obtained for the first time from Mn enriched Si/SiO2 structure. Si+ or Ar+ stimulated knock-on implantation through 20 nm Mn film with the subsequent annealing was used for EL device fabrication. Devices exhibit bright emission band at the 2.06 eV. The position does neither depend on implanted ion dose nor annealing procedure. EL is visible by naked eye even at current density as low as 1.5x10-6 Acm-2. Continuous wave external quantum efficiency 1.1x10-3 and power efficiency 1.5x10-5 have been achieved.