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We report the fabrication of buried contact solar cells using porous silicon as sacrificial layer to create well-defined channels (for buried contacts) in silicon. In this paper, the salient features of the technology have been presented. No detrimental effect was found in the performance of buried contact solar cell with partially filled contact area compared to the solar cells having conventional planar contacts. However, a marked difference in the short circuit current density was seen when channel was fully filled with metal by screen printing, without degradation in the open-circuit voltage. It is expected that improved processing in combination with optimized buried metallic contact parameters may yield higher efficiencies that may result in substantial decrease in solar cell cost.

The influence of the emitter thickness on the photovoltaic properties of monocrystalline silicon solar cells with porous silicon was investigated. The measurements were carried out on n + p silicon junction whose emitter depth was varied between 0.5 and 2.2 μm. A thin porous silicon layer (PSL), less than 100 nm, was formed on the n + emitter. The electrical properties of the samples with PS were improved with decrease of the n + p junction depth. Our results demonstrate short-circuit current values of about 35–37 mA/cm 2 using n + region with 0.5 μm depth. The observed increase of the short-circuit current for samples with PS and thin emitter could be explained not only by the reduction of the reflection loss and surface recombination but also by the additional photogenerated carriers within the PSL. This assumption was confirmed by numerical modeling. The spectral response measurements were performed at a wavelength range of 0.4–1.1 μm. The relative spectral response showed a significant increase in the quantum efficiency of shorter wavelengths of 400–500 nm as a result of the PS coating. The obtained results point out that it would be possible to prepare a solar cell with 19–20% efficiency by the proposed simple technology.

The performance improvement of solar cells due to the formation of a porous silicon layer on deep-junction n+/p silicon structures has been investigated. The photovoltaic properties of two identical sample groups with and without porous silicon layer are compared. More than a 50% improvement in Isc and about a 5% increase in Voc was demonstrated in structures with PS layer. No change in the fill factor was observed. The performance of the porous silicon solar cell has been found to be sensitive to the PS layer thickness. Optimal thickness was determined using the electrical measurement. The main result is that the photovoltaic energy conversion efficiency of solar cells can be increased by the PS layer. This low-cost PS formation process can be applied in the photovoltaic cell technology as a standard procedure. © 1997 Elsevier Science S.A.

Lightly-doped-drain MOS transistors with an inverse-T-gate and an active polysilicon spacer are investigated. The application of these devices in VLSI integrated circuit fabrication is examined from a practical point of view. It is shown that in comparison to the minimum gate length of a conventional transistor the designed gate length can be decreased, with the double spacer width. The results of the ring-oscillator measurements show that the increase in overlap capacitance is not a restriction for circuit application of these devices.

Resonant Raman scattering by ion beam synthesized in silicon matrix ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase is studied. The samples are prepared with the implantation of $^{24}\mathrm{Mg}^{+}$ ions with dose $4\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and with two different energies 40 and $60\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ into (100)Si substrates. The far infrared spectra are used as criteria for the formation of the ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase. The Raman spectra are excited with different lines of ${\mathrm{Ar}}^{+}$ laser, with energies of the lines lying in the interval from $2.40\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2.75\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The resonant scattering can be investigated using these laser lines, as far as according to the ${\mathrm{Mg}}_{2}\mathrm{Si}$ band structure, there are direct gaps with energies in the same region. The energy dependences of the scattered intensities in the case of the scattering by the allowed ${F}_{2g}$ and the forbidden LO-type modes are experimentally obtained and theoretically interpreted. On the base of the investigation energies of the interband transitions in the ${\mathrm{Mg}}_{2}\mathrm{Si}$ are determined. It is found also that the resonant Raman scattering appears to be a powerful tool for characterization of a material with inclusions in it. In the particular case it is concluded that the ${\mathrm{Mg}}_{2}\mathrm{Si}$ phase is present in the form of a surface layer in the sample, prepared with implantation energy $40\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and as low-dimensional precipitates, embedded in the silicon matrix, in the sample, prepared with the higher implantation energy.

The apparent expression of MOST threshold voltage distribution with arbitrary mask-level gate length is obtained. It is shown that calculated and experimental distributions are in good agreement in the case of a short channel device.

Continuous layers and precipitates of the β-FeSi2 phase were formed by ion-beam synthesis followed by rapid thermal annealing. Two steps of Fe+ ion implantation in Si, at energies of 20 and 60 keV, were performed, using three different doses – 5×1015, 5×1016, and 1017 cm−2. The infrared spectra were used as a criterion for the formation of the β-FeSi2 phase. The refractive-index-energy dependences were calculated from the transmittance and reflectance spectra, using the general matrix method. From these dependences, the energy band gap and the energies of the higher-energy transitions in the vicinity of the gap were determined.

Interface and oxide characteristics of a O 2 +4% HCl grown SiO 2 after different type low temperature plasma treatment (He, H 2 , Ar) have been investigated. It is shown that all the plasmas used introduce radiation defects in the Si-SiO 2 structures: oxide fixed charge (in order of 10 11 cm −2 ) and interface acceptor states (shallow and deep with a density depending on the plasma regime). These defects strongly influence the scattering of electrons in the inversion channel. It is shown also that a partial annealing of the radiation defects in Si-SiO 2 structures caused by heavy-particle plasmas (e.g. Ar plasma) is typical of He- and H 2 -plasmas; H 2 plasma effect is stronger.

Combining measurements of inversion channel I-V and high frequency C - V characteristics it is shown that argon plasma treatment leads to an increase of positive fixed oxide charge and generation of deep acceptor-type interface states (with a charge density of about 10 11 cm −2 ) accompanied by a reduction of the density of shallow acceptor-type interface states and a decrease of the inversion layer mobility. The radiation induced oxide charge is in the order of (1–3.5) × 10 11 cm −2 depending on the oxide thickness. The mobility decrease and the plasma-introduced charges in the Si-SiO 2 structures are assumed mainly to be trivalent Si and non-bridging oxygen due to the radiation-induced fracture of weak and strained bonds in the oxide and at the interface. The temperature behaviour of the mobility indicates a dominance of Coulomb and surface potential fluctuation scattering. Hence a severe degradation of Si-SiO 2 structures after low-temperature argon plasma treatment is found.