The p recombination layer in tunnel junctions for micromorph tandem solar cells

A new tunnel recombination junction is fabricated for n–i–p type micromorph tandem solar cells. We insert a thin heavily doped hydrogenated amorphous silicon (a-Si:H) p + recombination layer between the n a-Si:H and the p hydrogenated nanocrystalline silicon (nc-Si:H) layers to improve the performance of the n–i–p tandem solar cells. The effects of the boron doping gas ratio and the deposition time of the p-a-Si:H recombination layer on the tunnel recombination junctions have been investigated. The current-voltage characteristic of the tunnel recombination junction shows a nearly ohmic characteristic, and the resistance of the tunnel recombination junction can be as low as 1.5 ·cm 2 by using the optimized p-a-Si:H recombination layer. We obtain tandem solar cells with open circuit voltage V oc = 1.4 V, which is nearly the sum of the V oc s of the two corresponding single cells, indicating no V oc losses at the tunnel recombination junction.     

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.     

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.     

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.     

Simultaneous luminescence due to excitons,condensation and free electrons phases in silicon

Using electrical injection in silicon P⁺πN⁺ structures at low temperature, we observe simultaneously recombination lines from condensation, free excitons and free electrons phases. The possible simultaneous observation of the three phases (condensation, excitons, free electrons) is therefore demonstrated in silicon. The actual temperature of the sample is discussed with the help of recombination oscillations and current-voltage characteristics.     

Electrical and optical properties of nanowires based solar cell with radial p-n junction

In our studies the absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by the FDTD (Finite-Difference Time-Domain) method. It is shown that the proportion of reflected light in periodic structures is smaller than in case of thin films. The experimental results showed the light reflectance in the spectral range of 400–900 nm lower than 1% and it was significantly lower in comparison with surface texturing by pyramids or porous silicon.Silicon nanowires on p-type Si substrate were formed by the Metal-Assisted Chemical Etching method (MacEtch). At solar cells with radial p-n junction formation the thermal diffusion of phosphorus has been used at 790 °C. Such low temperature ensures the formation of an ultra-shallow p-n junction. Investigation of the photoelectrical properties of solar cells was carried out under light illumination with an intensity of 100 mW/cm². The obtained parameters of NWs' solar cell were I_sc = 22 mA/cm², U_oc = 0.62 V, FF = 0.51 for an overall efficiency η = 7%. The relatively low efficiency of obtained SiNWs solar cells is attributed to the excessive surface recombination at high surface areas of SiNWs and high series resistance.     

Phonon-assisted radiative electron-hole recombination in silicon quantum dots

The temperature dependence of the photoluminescence (PL) spectrum of silicon quantum dots (QDs) is studied both theoretically and experimentally, and the time of the corresponding electron-hole radiative recombination is calculated. The dependence of the recombination time on the QD size is discussed. The experiment shows that the PL intensity decreases by approximately 60% as the temperature increases from 77 to 293 K. The calculated characteristic recombination time has only a weak temperature dependence; therefore, the decrease in the PL intensity is associated primarily with nonradiative transitions. It is also shown that the phonon-assisted radiation is much more efficient than the zero-phonon emission. Moreover, the zero-phonon recombination time depends on the QD radius R as R⁸, whereas the phonon-assisted recombination time depends on this radius as R³.     

半导体深能级瞬态谱中多子脉冲下的少子陷阱响应

在一个Si中掺Aup⁺n结的多子脉冲下深能级瞬态谱(DLTS)中,发现了一个少子峰信号。给出了这一现象的主要实验结果,并做了系统的物理分析。这是p⁺n结中高掺杂一侧的自由少数载流子尾在自建势所张开的空间电荷区中被少子陷阱俘获后,再发射的结果。 关键词：     

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.     

Radial junction silicon solar cells with micro-pillar array and planar electrode interface for improved photon management and carrier extraction

We demonstrate radial p-n junction silicon solar cells with micro-pillar array with higher short-circuit current and open-circuit voltage than comparable planar silicon solar cells. Micro-pillar array, fabricated by RIE, acts as an effective anti-reflection coating for visible light with less than 6% reflection. Compared to devices with planar surface, devices with micro-pillar array show a 27% enhancement in short circuit current. The radial p-n junction of the micro-pillars also improves extraction probability of the photogenerated carriers, which further increases the short circuit current. Typically, micro-pillar solar cells suffer from high recombination losses at the Si/metal interface, resulting in poor V_OC. Our devices prevent these recombination losses by planarizing the Si/metal interface, leading to an open circuit voltage of 622?mV, the highest ever reported for micro-pillar solar cells. This planarized contact also reduces the series resistance associated with radial junctions, leading to series resistance of ≤0.50?Ω-cm² and fill factors up to 76.7%.     

Surface recombination velocity in a silicon optical waveguide

Measurements of the varying infrared absorption by free carriers in a silicon waveguide during intermittent electron bombardment are used to study the surface recombination velocitys. The same values for s are obtained for heat-treated and untreated samples, which supports the theory that electron beam irradiation in itself has a dehydrating effect. Other experiments show thats is not dependent on the energy of the impinging electrons in the range 16–23 keV. Finally, the temperature dependence ofs in gold-doped silicon is estimated. Ifs is written in the forms=s ₀(293/T)^x,x is found to be 2.1±0.2 in the temperature interval 261K≦T≦309K.     

The Numerical Simulation of the Nanosecond Switching of a <Emphasis Type="Italic">p</Emphasis>-SOS Diode

Abrupt high-density reverse current interruption has been numerically simulated for switching from forward to reverse bias in a silicon p⁺P₀n⁺ structure (p-SOS diode). It has been shown that the current interruption in this structure occurs as a result of the formation of two dynamic domains of a strong electric field in regions in which the free carrier concentration substantially exceeds the concentration of the doping impurity. The first domain is formed in the n⁺ region at the n⁺P⁰ junction, while the second domain is formed in the P⁰ region at the interface with the p⁺ layer. The second domain expands much faster, and this domain mainly determines the current interruption rate. Good agreement is achieved between the simulation results and the experimental data when the actual electric circuit determining the electron–hole plasma pumping in and out is accurately taken into account.     

Structure and transport mechanisms of Si/porous Si n-p junctions prepared by liquid phase epitaxy

Heterojunction devices of n-Si/p-PSi were fabricated by growing n-Si films onto p-type porous Si substrates by liquid phase epitaxy. The structure of the grown films was checked using scanning electron microscopy and X-ray diffraction spectroscopy. X-ray diffraction measurements showed that the grown films have monocrystalline structure oriented along (1 1 1) direction with mainly cubic phase. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured over the temperature range from 298 to 398 K. The analysis of the dark I-V characteristics of n-Si/p-PSi at several temperatures is done to elucidate the conduction mechanisms and the evaluation of the heterojunction parameters is presented. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V ≤ 0.4 V) the forward current is dominated by the recombination at the porous silicon side of the space charge region. In the 0.5 V ≤ V ≤ 1.4 V region, the current transport is due to the space charge—limited current mechanism dominated by a single trapping level of energy 0.41 eV. The reverse current is considered to be mainly generated in the depletion region of the porous silicon. The capacitance-voltage results confirm an abrupt junction with a homogenous distribution of the impurities inside the space charge region. Information on the depletion region, built-in voltage and net carrier concentration were obtained from the dark C-V characteristics.     

Properties of magnesium silicate doped with chromium in porous silicon

Forsterite doped with Cr⁴⁺ ions is prepared in silicon-based structures according to a simple technique. These structures are of interest due to the characteristic luminescence in the near-IR range. Forsterite is synthesized by impregnation of porous silicon layers on n⁺-Si and p⁺-Si substrates with subsequent annealing in air. A photoluminescence response at a wavelength of 1.15 μm is observed at room temperature in porous silicon layers doped with magnesium and chromium for which the optimum annealing temperature is close to 700°C. The photoluminescence spectrum of porous silicon on the p⁺-Si substrate contains a broad band at a wavelength of approximately 1.2 μm. This band does not depend on the annealing temperature and the magnesium and chromium content and is most likely associated with the presence of dislocations in silicon. The experimental EPR data and eletrical properties of the structures are discussed. It is found that layers of pure porous silicon and chromium-doped porous silicon on n⁺-Si subtructures exhibit indications of discrete electron tunneling.     

Electrical and optical properties of composites based on carbazole derivatives and silicon particles

The electrical and optical properties of polymer-silicon composites with particles incorporated by different means have been studied. It is shown that both when silicon particles are embedded in a carbazole-containing polymer matrix and in the case of a pure polymer, the I–V characteristics are nonlinear and asymmetric (the I–V characteristics of the carbazole-containing polyorganosiloxane, which has silicon atoms in the monomer link, behave in a more symmetric pattern). In all cases, the I-V characteristics can be fitted with power laws, I(V) ～ V ^p , with three different slopes for different voltage intervals, which remainds one of the pattern typical of the mechanism of space-charge-limited currents. It is shown that, in its luminescent properties, the carbazole-containing polyorganosiloxane is similar to a carbazole-containing polymer matrix with embedded silicon particles. The results obtained argue for charge transfer between the polymer and silicon nanoparticles if they are embedded in the matrix and for an formation of an interchain charge-transfer complex in the case of chemically bound silicon.     

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     

Residual non-idealities in the almost ideal silicon p-n junction

The reproducible, mass production of almost ideal silicon p-n junctions has allowed two new phenomena to be discovered: a pure generation without recombination, and a slow capacitance-free current transient. Our present knowledge of these phenomena is reviewed and speculations about the centres responsible for them are discussed; these centres seem to be connected to ultimate, unavoidable properties of the silicon p-n junction rather than to unwanted impurities.     

Inclusiveπ +/π - ratio in meson-proton reactions and the quark recombination model

The inclusiveπ ⁺/π ^- inπ ^± p andK ^± p reactions at different incident energies has been compared to that ofpp reactions. Up to ? 100 GeV/c a significant dependence on the beam quantum numbers has been observed for this ratio in the target fragmentation region. Since the naive quark recombination model cannot account for this effect, we discuss qualitatively valence quark annihilation with subsequent recombination as an additional mechanism.     

The spectrum and decay of the recombination radiation from strongly excited silicon

The spectral distribution of the recombination radiation from silicon during and after excitation by a Q-switched ruby laser has been measured and analyzed. The interpretation assumes a third-order (Auger) recombination process and a simple parabolic band structure. It takes into account the heating of the sample at the surface and the reduction of the band gap due to the high carrier density. Measurements of the spectral distribution as a function of time gives a value of the Auger transition rate factor γ₃ = 2·10⁻³¹ cm⁶sec⁻¹.     

Thermal annealing induced photocarrier radiometry enhancement for ion implanted silicon wafers

An experimental study on the photocarrier radiometry signals of As⁺ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion implantation dose (1×10¹¹--1×10¹⁶/cm²), implantation energy (20--140 keV) and subsequent isochronical annealing temperature (500--1100 du are investigated. The results show that photocarrier radiometry signals are greatly enhanced for implanted samples annealed at high temperature, especially for those with a high implantation dose. The reduced surface recombination rate resulting from a high built-in electric field generated by annealing-activated impurities in the pn junction is believed to be responsible for the photocarrier radiometry signal enhancement. Photocarrier radiometry is contactless and can therefore be used as an effective in-line tool for the thermal annealing process monitoring of the ion-implanted wafers in semiconductor industries.