Microwave photoconductivity relaxation time in a bifacial silicon solar cell base in the vicinity of a p-n junction

Microwave photoconductivity relaxation time depending on light intensity is studied in n ⁺-p-p ⁺ silicon solar cells. The results from experiments performed under conditions of open-circuit and short-circuit currents are in agreement with the simulated data. The relaxation times of microwave photoconductivity are found for a part of the base region adjacent to the n ⁺-p junction.     

Analysis of the R0A product in n+-p Hg1−xCdxTe photodiodes

The influence of different junction current components (diffusion current for radiative and Auger 7 recombination mechanisms, tunneling and depletion layer currents) on the R₀A product of n⁺-p -Hg_1−xCd_xTe photodiodes is considered. The considerations are carried out for the 77–300 K temperature region and 1–15 μm cutoff wavelength. Optimum doping concentrations in the p-type region of n⁺-p abrupt junctions are determined, taking into account the influence of the tunneling current and of a fixed surface charge density of the junction passivation layer. Results of calculations are compared with experimental data reported by many authors. An attempt is made to explain the discrepancy between theoretical calculations and experimental data.     

Polycrystalline silicon S-diode fabricated using phosphorus thermal diffusion along grain boundaries

Electrical activity of grain boundaries (GB) in polycrystalline silicon films can stand duty as an additional factor of action on its properties. At present paper it has been studied polycrystalline silicon epitaxial films grown by CVD-method at low-resistivity n ⁺-type poly-Si substrates. A p ⁺-n junction of 0,5 m deep was formed by ion implantation of boron. The effect of thermal annealing (TA) on I-V characteristics of the p ⁺-n-n ⁺ structures was studied. It was founded that the region with negative resistivity is appeared in I-V characteristic after TA in vacuum at 800°C for 1 hour. Investigations by means of C-V and temperature characteristics of samples show that the S-image of the I-V characteristics is caused by phosphorus diffusion along GB that give rise to conduction of the charge carriers along GB. For the first time it was shown the opportunity of the creation of low-cost poly-Si S-diode by TA.     

Peculiarities of the capacitance-voltage characteristic of a photoelectric solar energy convertor based on a silicon p-n junction with a porous silicon antireflection coating

Experimental results on the high-frequency capacitance-voltage characteristic of a photoelectric solar energy converter based on the n ⁺-p junction with a thin porous silicon film on the frontal surface are considered. It is shown that the capacitance-voltage characteristic is determined by the surface metal-insulator-semiconductor (MIS) structure formed as a result of growing of a porous silicon layer by electrochemical anode etching. The effective thickness of the insulator layer of the MIS structure, the impurity concentration in its semiconductor region, and the density of surface states are determined.     

Photoluminescence and EPR of porous silicon formed on <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript> and <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript> single crystals implanted with boron and phosphorus ions

The effect of combined doping by shallow donor and acceptor impurities on boosting the quantum yield of porous-silicon photoluminescence (PL) in the visible and near IR range was studied using phosphorus and boron ion implantation. Nonuniform doping of samples and subsequent oxidizing annealing were performed before and after porous silicon was formed on silicon single crystals strongly doped by arsenic or boron up to ≈10¹⁹ cm^?3. The concentration of known P_b centers of nonradiative recombination was controlled by electron paramagnetic resonance. It is shown that there is an optimal joined content of shallow donors and acceptors that provides a maximum PL intensity in the vicinity of the red part of the visible spectrum. According to estimates, the PL quantum yield in the transitional n ⁺⁺-p ⁺ or p ⁺⁺-n ⁺ layer of porous silicon increases by two orders of magnitude as compared to that in porous silicon formed on silicon not subjected to ion irradiation.     

Characteristics of a photovoltaic X-ray detector based on a GaAs epitaxial structure

The characteristics of a photovoltaic X-ray detector based on the GaAs p ⁺-n-n′-n ⁺ epitaxial structure grown using gas-phase epitaxy are studied. Typical current-voltage and capacitance-voltage characteristics of the epitaxial structures are analyzed together with the built-in electric field profile in the n-GaAs depleted region. The efficiency of charge accumulation in the photovoltaic detector is measured for zero bias and for a bias voltage of 17 V. It is shown that the GaAs-based photovoltaic X-ray detector can operate with zero bias voltage at room temperature. The sensitivity of the detector is measured as a function of the effective energy of X-rays and the angle of incidence of X-ray photons.     

Pulse characteristics of Hg0.8Cd0.2Te n +-p junctions

The pulse characteristics of Hg_0.8Cd_0.2Te n ⁺-p junctions are investigated. It is shown that the shape of the voltage pulse appearing in a junction on passage of a forward (reverse) current is determined by the recombination (generation) of nonequilibrium electrons in the hole region. An increase in the current pulse causes the appearance of an electric field, which draws electrons into the interior of the base region, and leads to variation of their lifetime because of the complex structure of the n ⁺-p junction. Zh. Tekh. Fiz. 67, 130–133 (July 1997     

Structural and optical properties of porous silicon prepared from a p +-epitaxial layer on n-Si(111)

The structural and optical properties of porous silicon prepared by anodic etching of an n-Si(111) wafer with a p ⁺-homoepitaxial layer on one side are studied by scanning electron microscopy and multiple-crystal X-ray diffraction. A considerable difference between the microstructures on the sides of the wafer is found. Upon aging for 4.5 months, diffraction peaks of the por-Si structures shift from that of the substrate by δθ = ?42″ for the n-Si porous layer and ?450″ for the p ⁺-Si porous layer. The photoluminescence band associated with the p ⁺-layer is twice as narrow as the band associated with the n-layer and is shifted toward shorter wavelengths (higher energies) by 0.4 eV, with the intensities of the bands being the same.     

Quantum efficiency and responsivity of InSb photodiodes utilizing the Moss-Burstein effect

In this work a detailed analysis of the quantum efficiency of InSb n⁺-p photodetectors produced by liquid phase epitaxy is given, in the case when the n⁺ region is doped to such a level that the Moss-Burstein effect plays an important role. Our starting point was the theoretically determined coefficient of intrinsic absorption and derived expressions for the generated photocurrent in the n⁺ region, depletion layer and p-phase of the photodetector. The results are presented in the form of graphical dependence of the quantum efficiency on the wavelength, with the electron concentration in the n⁺ layer as a parameter.     

Spin-dependent recombination in a silicon p-n junction

Like the spin-denendent photoconductivity in pure silicon, the current of a silicon n⁺-p junction is found to be affected by electron spin resonance. The experiment shows that the same centers are responsible for the recombination in the diode and in pure silicon, that only the recombination in the space-charge region of the junction is spin-dependent and that the effect in this region is very large. A tentative model for the electron-hole recombination in silicon is proposed.     

Modification of the surface state and doping of CdTe and CdZnTe crystals by pulsed laser irradiation

The photoelectric and electrical properties of high-resistivity p-like CdTe and Cd_0.96Zn_0.04Te single crystals and barrier structures on their base before and after laser irradiation in different conditions are studied. Irradiation of samples with nanosecond ruby laser pulses was carried out in two different ways. In the first case, the Cd(Zn)Te crystals were subjected to laser action directly from the surface and irradiation within a certain range of intensities resulted in a decrease in the surface recombination rate and increase in the photoconductivity signal. The surface region with a wider bandgap in CdZnTe crystals was formed. In the second case, the samples were irradiated from the side pre-coated with a relatively thick In dopant film and it caused rectification in the I-V characteristics as a result of laser-induced doping of the thin Cd(Zn)Te surface region and formation of a built-in p-n junction. The application of the fabricated M-p-n structured In/Cd(Zn)Te/Au diodes for X-ray and γ-ray detectors is discussed.     

Positron annihilation from excited states of [X-e+] systems

The relative probabilities for the radiative de-excitation 2p₊ → ls₊ versus 2γ-annihilation for the hdot; ns²np⁶2p₊, ²P state of the [X^-e⁺] system with X = F, Cl, Br, and I are presented. It is shown that a positron captured into a 2p₊ orbital undergoes annihilation with electrons of the system instead of radiative transition to the ground state of the [X^-e⁺] system.     

Characteristics of the formation of radiation defects in silicon structures

The method of deep-level transient spectroscopy is used to investigate aspects of the formation of radiation defects in silicon p ⁺-n diffusion structures when bombarded by accelerated electrons. It is shown that for base thicknesses of the p ⁺-n structures in the range 0.2–0.6mm a substantial change in the concentration of the radiation defects formed in this way is observed, having a maximum at 0.25 mm. Below 0.2 mm and above 0.6 mm the concentration of radiation defects exhibits a weak dependence on base thickness. The observed effect is explained by variation of the relative concentrations of vacancies and interstitial silicon atoms in the base during formation of p ⁺-n pairs. Zh. Tekh. Fiz. 69, 121–123 (January 1999)     

Potential of chemical rounding for the performance enhancement of pyramid textured p-type emitters and bifacial n-PERT Si cells

We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of AlO_x- and AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured p⁺-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of AlO_x layers on pyramid textured p⁺-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance (R_SW) from ∼2.5 to ∼3.7% for the AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ∼60 and ∼100 Ω/sq p⁺-emitters is reduced by 0.8 and 0.6 mA/cm², respectively under front p⁺-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with ∼60 and ∼100 Ω/sq p⁺-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ∼100 Ω/sq p⁺-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.     

Effect of the <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junction breakdown mechanism on the Er<Superscript>3+</Superscript> ion electroluminescence intensity and excitation efficiency in Si: Er epitaxial layers grown through sublimation molecular beam epitaxy

A series of Si: Er/Si light-emitting diode structures with a smoothly varying p-n junction breakdown mechanism, grown through sublimation molecular-beam epitaxy, is used to investigate the effect of the breakdown mechanism on the electroluminescence of the structures. The maximal intensity and excitation efficiency of room-temperature Er³⁺ ion electroluminescence are shown to be attained in diode structures with a mixed breakdown mechanism.     

Reflectance spectrum of lithium hydride at the Li K-absorption edge

Reflectance spectra of LiH single crystals are measured at the Li⁺K- absorption edge for the first time. The ?₂ spectrum shows a prominent peak at 57.8 eV followed by several structures at the high energy side. We attribute the peak to a transition from the Li⁺ 1s to the n = 1 core exciton state associated with the p-like conduction band.     

Radiation-induced conduction in quantum-confined p +-n silicon junctions

Electron-beam diagnostics are used to study the radiation-induced conduction of supershallow p ⁺-n silicon junctions obtained by nonequilibrium boron diffusion. Current-voltage (I–V) characteristics of radiation-induced conduction of a both forward-and reverse-biased p ⁺-n junction are demonstrated for the first time, which has been made possible by the presence of self-organized transverse quantum wells inside a supershallow p ⁺ diffusion profile. The variation of the dark-current I–V characteristics with electron irradiation dose shows that formation of self-organized longitudinal quantum wells inside supershallow p ⁺ diffusion profiles favors an increase of the breakdown voltage in p ⁺-n silicon junctions. Fiz. Tverd. Tela (St. Petersburg) 41, 1871–1874 (October 1999)     

Structure and stability of SiBn+ AND CBn+ (n = 1–4)

The structures and binding energies of small boron-rich clusters are studied using correlated wave functions and polarization basis sets. Carbon is the central atom in CB_n⁺, while SiB_n⁺ prefers planar boron networks with silicon as one of the edge atoms. These ground state structures can be explained by differences in the electronegativities of the component elements. The various fragmentation channels of SiB_n⁺ are also examined using binding energy differences.     

Effect of high doses on the Si <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> x-ray emission spectra of silicon implanted with iron ions under steady-state conditions

The effect of high doses on p-and n-type silicon samples implanted with Fe⁺ ions under steady-state conditions (implantation energy, 100 keV; ion current density, 0.6–0.8 μA/cm²; irradiation dose, 10¹⁴–10¹⁶ ions/cm²) is investigated using Si L _{2, 3} x-ray emission spectroscopy (the 3d3s → 2p electronic transition). An analysis of the Si L x-ray emission spectra of the silicon samples is performed by comparison with the spectra of reference materials and the spectra of silicon samples implanted with Fe⁺ ions in a pulsed mode. The Si L x-ray emission spectra are simulated by the molecular dynamics and full-potential linearized augmented-plane-wave (FLAPW) methods. It is revealed that the effect of high doses under steady-state conditions of Fe⁺ ion implantation into the semiconductor crystal matrix exhibits specific features: the disordering of the structure and partial amorphization of the sample from the surface deep into the bulk are more pronounced than those observed under conditions of pulsed ion implantation, although virtually no recrystallization of the sample at the threshold dose occurs. The most probable origins and mechanisms of the effect of high doses on the samples under investigation are discussed.     

First-Principles Study on the Electronic Structures for Y^3＋：PbWO4 Crystals

The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （GULP）. The calculated results indicate that in the lightly doped Y^3＋ ：PWO crystal, the main compensating mechanism is [2Ypb^＋ ＋ VPb^2-], and in the heavily doped Y^3＋ ：PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^＋, forming defect clusters of [2Ypb^＋ ＋Oi^2-] in the crystal. The electronic structures of Y3＋ ：PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.