Ion implantation of zinc sulphide

The passivation of argon sputter-etch induced electrically active defects on Ge, Si, and GaAs surfaces by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. A broad band of defect states, giving rise to non-linear Arrhenius plots, appears to be associated with the induced damage centres. For n-type Ge and p-type Si, a 20-min exposure to atomic hydrogen at 180°C is shown to neutralize the damage created by a 5-min, 6 kV (DC), Ar gas sputter-etch. For n-type GaAs a 1-h exposure at 250°C was sufficient, whilst n-type Si required a 1-h exposure to the hydrogen plasma at 300°C to passivate the damage. In each case, to remove the sputter-etch damage by thermal annealing required temperatures approximately 100°C higher, for periods of approximately 2 h.     

ZnO-based heterojunction light-emitting diodes on p-SiC(4H) grown by atomic layer deposition

Atomic layer deposition was used to grow n-type Al-doped ZnO (n-ZnO) and undoped ZnO (i-ZnO) layers on p-type 4H-SiC substrates, to fabricate n-ZnO/p-SiC and n-ZnO/i-ZnO/p-SiC heterojunction light-emitting diodes (LEDs). Electroluminescence (EL) from the n-ZnO/p-SiC LED originated from radiative recombination of donor–acceptor pairs in SiC due to the predominant electron injection from n-ZnO into p-SiC. On the other hand, the n-ZnO/i-ZnO/p-SiC LED exhibited dominant ultraviolet (UV) emission at 393 nm from ZnO. This difference is attributable to the insertion of the undoped i-ZnO layer between n-ZnO and p-SiC, leading to the injection of holes from p-SiC and electrons from n-ZnO into the i-ZnO layer and thus the generation of UV EL from ZnO.     

Donor-hydrogen complexes in crystalline silicon

Summary Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing¹¹⁹Sb→¹¹⁹Sn source M?ssbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the M?ssbauer intensity associated with the trapping of hydrogen, even at low temperatures. This is interpreted as the formation of a component with a negligible recoilless fraction. The different M?ssbauer components were studied as a function of H dose, H-implantation temperature and annealing temperature. The data show that the visible component is associated with the well-known SbH complex, whereas the invisible component is associated with the formation of SbH _n (n≥2) complexes. We show that these complexes are in thermal equilibrium with a larger hydrogen reservoir (H ₂ ^* ), which governs their thermal stability. No Sb-H complexes are observed inp-type Si after H-implantation, in agreement with the current belief that hydrogen has a deep donor level in the gap. The microscopic structure of the various Sb-H and Sn-H complexes was studied with first-principles calculations using the pseudopotentialdensity-functional approach. The structure of the Sb-H complex is found to be similar to the P-H complex, with the H in an antibonding site of a Si atom neighbouring the Sb impurity. For SbH₂ three configurations are found with energies differing by less than ≈ 0.1 eV. We find that the reaction SbH+H≠SbH₂ is exothermic. We argue that the SbH₂ complexes are shallow donors, irrespective of the structure. Therefore, the formation of SbH₂ may depassivate the sample. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Preparation and characterization of the LiInSe2 thin films

Summary p-type LiInSe₂ films have been prepared by the rapid evaporation method onn-type Si andn-type GaP. Various characterization techniques such as the X-ray analysis, the Rutherford backscattering (RBS) analysis and the scanning electron microscopy were used to evaluated the quality of the films. The rectifications of the preliminary heterojunctions are demonstrated. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Defect studies in small CdTe clusters

We study Cd vacancy formation in prototype stoichiometric and non-stoichiometric CdTe clusters with and without passivation. For certain clusters like Cd₁₃Te₁₆, vacancy leads to severe distortion of the geometry due to propagation of defect. Annealing of the vacancy out of the cluster is observed in all unpassivated clusters. Passivated clusters retain their initial geometry and vacancy induced structural distortions are not seen in these clusters since the defect gets localized. Vacancy also induces intragap states. However, it was observed that the passivation of the dangling bonds created by the vacancy removes the intragap states. In an attempt to have CdTe clusters with extrinsic carriers, we substituted a Cd atom by its adjacent atoms Pd/Ag/In/Sn in these CdTe clusters. Substitutional doping of Cd by metal atoms increases the stability of unpassivated clusters. For certain clusters, metal atom doping leads to a half-metallic character. Pd/Ag-doped clusters are p-type semiconductors whereas In-doped clusters are n-type semiconductors. Sn doping in these clusters does not result in n-type semiconductors.     

Electrical transport properties of hydrogen-exposed p-type PbTe films

Hall coefficient and d.c. conductivity measurements were made on p-type PbTe epitaxial films exposed to molecular hydrogen gas at high pressures (100–500 psi) in the temperature range (100–300K). It is found that hydrogen converts p-type films to n-type at a pressure of about 300 psi. The results are explained by assuming that the action of hydrogen is to provide donor electrons.     

Electrically active defect annealing in neutron and in ion-damaged Si

Hall effect and electrical conductivity measurements of defect annealing in 1 ohm-cm n-type and 2 ohm-cm p-type silicon were made following neutron irradiation at ～50°C. Measurements were also made following 400-keV B¹¹ ion implantation into a 100 ohm-cm n-type Si substrate. As the neutron fluence is increased the electrical effects of the damage eventually outweigh those of the chemical dopants, and further changes in the electrical properties become small. Conversely, significant electrical recovery upon annealing begins only when the electrical effects of the remaining damage become comparable to those of the chemical dopants. This condition will occur at higher anneal temperatures for higher fluence irradiations. The neutron fluence dependence of the damage and the annealing is interpreted in terms of the neutron energy per cm³. E, spent in atomic processes divided by the number/cm³, N, of electrically active dopants. When E/N ≤ 0.5 keV the electrical measurements show that the predominant defect annealing occurs below 400°C. However, when E/N > 0.5 keV electrical measurements emphasize the annealing at temperatures > 400°C. After 500°C annealing, energy levels in neutron damaged Si are observed at E_v +0.1 and E_v +0.15 eV in p-type and at E_c -0.33 eV in n-type Si. Application of the E/N criteria to room temperature implant-doped Si predicts that the electrical effects will be dominated by lattice damage even if all the implanted ions are substitutional.     

多孔硅的光生伏特效应

多孔硅(PS)的可见光致发光的发现[1],引起人们对PS的光电特性及其在光电器件上应用可能性的广泛探索.已报道用PS制成发出可见光的电致发光器件[2]及高灵敏的光探测器件[3].本文将报道PS层与金属接触,光照时能出现很强的光生伏特效应,利用这一特性有可能制成高效的光电转换器件.     

Relaxation into tunnel induced nonequilibrium states in metal-oxide semiconductor structures

The relaxation of a metal-oxide semiconductor structure from deep depletion towards a tunnel-induced non-equilibrium steady state is addressed in this work. A simple model was constructed, taking into account thermal generation, tunneling of both types of carriers and impact ionization. Experimental results obtained on p-and n-type Si substrates and oxides thinner than 6.5 nm are shown to be well fitted by the proposed model. A map describing the possible behavior patterns for a structure with given oxide thickness and effective generation velocity is presented. Fiz. Tverd. Tela (St. Petersburg) 41, 862–864 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Hydrogenation effect on enhancement of photoluminescence of Er and Si nanocrystallites in Er-doped SiO2 synthesized by laser ablation

Significant enhancement of photoluminescence (PL) was attained for Er ions and Si nanocrystallites (nc-Si) in SiO₂ films by two kinds of hydrogenation, using H₂ molecules or H atoms. Er-doped SiO₂ films containing Er impurities and a high density of nc-Si were fabricated by laser ablation of Er films deposited on Si substrate in an O₂ gas atmosphere, followed by annealing at high temperatures in flowing Ar gas. Hydrogenation at 300–500 °C was found to effectively increase the PL intensity of Er ions as well as that of nc-Si. In particular, the hydrogen atom treatment dramatically shortens the hydrogenation time for the enhancement of Er PL compared to the hydrogen molecule treatment. Spectra of electron spin resonance showed a decrease in residual defects, namely, P_b-type defects located at the interfaces between nc-Si and SiO₂ by hydrogenation. These results clearly show the effectiveness of hydrogen passivation for Si nanostructures; i.e., the increase in the Er PL and nc-Si PL due to hydrogen passivation of the nonradiative recombination centers located at the interfaces between nc-Si and SiO₂. PACS 78.67.Bf; 71.20.Eh; 76.30.Mi; 81.15.Fg     

Role of zinc and nickel impurities in high-temperature superconductors

The local changes produced in the electronic structure and their effect on the physical properties of the superconducting and normal phases when zinc and nickel are substituted for copper are examined on the basis of a multiband p-d model. It is shown that strong electronic correlations suppress the S=1 configuration of Ni²⁺ and cause the superposition of the S=1/2 and S=0 states of nickel. The change in the density of states in p-and n-type systems is studied, and the peculiarity of Zn impurity for p-type systems and Ni impurity for n-type systems is shown. The universal dependence of the T _c on the residual resistance in lightly doped superconductors and deviations from it in optimally doped systems are discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 596–600 (April 1999)     

Isomer-shift of interstitial and substitutional iron in silicon and germanium

We describe results from in-beam Mössbauer implantation measurements for⁵⁷Fe inn-type Si, inp-type Si, and in Ge. Ab initio calculations for the contact densities from density functional theory in the local-density approximation are presented and their results are employed to locate the type of position of Fe in the lattice of the host. Thus the different spectral features corresponding to interstitial and substitutional Fe in Si and Ge are unambiguously identified.Dedicated to U. Gonser on the occasion of his 70th birthday     

Carrier dynamics and terahertz photoconductivity of doped silicon measured by femtosecond pump-terahertz probe spectroscopy

The carrier dynamics and terahertz photoconductivity in the n-type silicon (n-Si) as well as in the p-type Silicon (p-Si) have been investigated by using femtosecond pump-terahertz probe technique. The measurements show that the relative change of terahertz transmission of p-Si at low pump power is slightly smaller than that of n-Si, due to the lower carrier density induced by the recombination of original holes in the p-type material and the photogenerated electrons. At high pump power, the bigger change of terahertz transmission of p-Si originates from the greater mobility of the carriers compared to n-Si. The transient photoconductivities are calculated and fit well with the Drude-Smith model, showing that the mobility of the photogenerated carriers decreases with the increasing pump power. The obtained results indicate that femtosecond pump-terahertz probe technique is a promising method to investigate the carrier dynamics of semiconductors.     

Theoretical investigation on the passivation layer with linearly graded bandgap for the amorphous/crystalline silicon heterojunction solar cell

Passivation layer with linearly graded bandgap (LGB) was proposed to improve the performance of amorphous/crystalline silicon heterojunction (SHJ) solar cell by eliminating the large abrupt energy band uncontinuity at the a‐Si:H/c‐Si interface. Theoretical investigation on the a‐Si:H(p)/the LGB passivation layer(i)/c‐Si(n)/a‐Si:H(i)/a‐Si:H(n⁺) solar cell via AFORS‐HET simulation show that such LGB passivation layer could improve the solar cell efficiency (η) by enhancing the fill factor (FF) greatly, especially when the a‐Si:H(p) emitter was not efficiently doped and the passivation layer was relatively thick. But gap defects in the LGB passivation layer could make the improvement discounted due to the open‐circuit voltage (V_OC) decrease induced by recombination. To overcome this, it was quite effective to keep the gap defects away from the middle of the bandgap by widening the minimum bandgap of the LGB passivation layer to be a little larger than that of the c‐Si base. The underlying mechanisms were analysed in detail. How to achieve the LGB passivation layer experimentally was also discussed. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Secondary ion mass spectrometry measurements of deuterium penetration into silicon by low pressure RF glow discharges

Abstract

Using secondary ion mass spectrometry (SIMS) the penetration of deuterium into Si(100) substrates as a result of exposure to deuterium low pressure rf discharges has been determined as a function of exposure time, thermal contact of the Si wafers to the substrate electrode, substrate doping, and discharge pressure. For undoped (100) single crystal Si exposed without intentional heating to a 25 m torr D₂ plasma for 1 min the deuterium concentration in the near-surface region (0—30 nm) approaches 10²¹ at.cm^?3. It drops off with depth, but is still greater than 10¹⁷ at.cm.^?3 at a silicon depth of 200 nm. The large penetration depth, the observation that lowering the substrate temperature decreases the rate of deuterium uptake, and the dependence of deuterium penetration on the substrate doping type indicate that hydrogen diffusion is of primary importance. The presence of a 50 nm thick oxide layer on the Si substrate during plasma exposure lowers the deuterium near-surface concentration in the Si substrate by about three orders of magnitude, while the presence of 10 nm of thermal oxide reduces the deuterium uptake only insignificantly. Heavily B and As doped polycrystalline Si show less deuterium penetration, while undoped polycrystalline Si shows more deuterium uptake than undoped single crystal Si for the same plasma treatment.     

Positron lifetime measurements inn- andp-type silicon

Positron lifetime measurements were carried out in four different samples of silicon, namelyn-type (P-doped) 75 Ωcm,n-type (Sb-doped) 0.018 Ωcm,p-type (B-doped) 60 Ωcm andp-type (B-doped) 0.02 Ωcm. The measurements were made at room temperature and at 77K. A positron lifetime of τ₁=(230±2) psec was found for all samples, independant of dopant or temperature. Paper A 17 presented at 3 rd Internat'l Conf. Positron Annihilation. Otaniemi, Finland (August 1973).     

The Effects of Thermal Treatments on Microstructure Phosphorus-Doped ZnO Layers Grown by Thermal Evaporation

The ZnO films doped with 3 wt% phosphorus (P) were produced by activating phosphorus doped ZnO (ZnO:P) thin films in oxygen (O₂) ambient at 600°C for 30, 60, 90 and 120 min, respectively. As-deposited films doped with phosphorus are highly conductive and n type. All the films showed p-type conduction after annealing, in an O₂ ambient atmosphere. The activation energies of the phosphorus dopant in the p-type ZnO under O₂ ambient gases indicate that phosphorus substitution on the O site yielded a deep level in the gap. With a further increase of the annealed durations, the crystalline quality of the ZnO:P sample is degraded. The best p-type ZnO:P film deposited at 600°C for 30 min shows a resistivity of 1.85 Ω cm and a relatively high hole concentration of 5.1 × 10¹⁷cm^–3 at room temperature. The films exhibit a polycrystalline hexagonal wurtzite structure without preferred orientation. The mean grain sizes are calculated to be about 60, 72, 78, 85 and 90 nm for the p-type ZnO films prepared at 600°C for 30, 60, 90 and 120 min, respectively. Room temperature photoluminescence (PL) spectra of the ZnO film exhibit two emission bands — paramount excitonic ultraviolet (UV) emission and weak deep level visible emission. The excellent emission from the film annealed at 600°C for 30 min is attributed to the good crystalline quality of the p-type ZnO film and the low rate of formation of intrinsic defects at such short duration. The visible emission consists of two components in the green range.     

Piezospectroscopic study (78°K) of radiation- produced absorption bands in Si†

Abstract

A detailed study has been made on two sharp sub-bands, 3.45 μ (2900 cm^?1) and 3.61 μ (2765 cm^?1) of the 3.3 μ broad defect absorption band in irradiated Si. Our results indicate that the 3.45 μ and 3.61 μ bands are observed in all types of Si (n-, p-type, and intrinsic) subjected to fast neutron reactor irradiation. Spectra were measured at 78 °K under the effect of a variable uniaxial compressive stress with polarized light. A relatively large dichroism is observed for all three stress directions ?100?, ?110?, and ?111?. We also confirm that both sharp bands exhibit splitting and energy shifts under the action of stress. The model of the divacancy defect given by Watkins and Corbett⁽⁵⁾ has been utilized to explain the data. The dichroism can be accounted for by the effects of Jahn-Teller alignment which arises from the strong bonding of nearest neighbor atoms of the divacancy. The splittings of the bands are small indicating that the Jahn-Teller distortion is little altered in the ground and excited states. The splittings appear to be most sensitive to stress along the vacancy-vacancy axis and a tentative model for the transitions is given.     

Extremely low surface recombination in 1 Ω cm n‐type monocrystalline silicon

A key requirement in the recent development of highly efficient silicon solar cells is the outstanding passivation of their surfaces. In this work, plasma enhanced chemical vapour deposition of a triple layer dielectric consisting of amorphous silicon, silicon oxide and silicon nitride, charged extrinsically using corona, has been used to demonstrate extremely low surface recombination. Assuming Richter's parametrisation for bulk lifetime, an effective surface recombination velocity S_eff = 0.1 cm/s at Δn = 10¹⁵ cm^–3 has been obtained for planar, float zone, n ‐type, 1 Ω cm silicon. This equates to a saturation current density J_0s = 0.3 fA/cm², and a 1‐sun implied open‐circuit voltage of 738 mV. These surface recombination parameters are among the lowest reported for 1 Ω cm c‐Si. A combination of impedance spectroscopy and corona‐lifetime measurements shows that the outstanding chemical passivation is due to the small hole capture cross section for states at the interface between the Si and a‐Si layer which are hydrogenated during nitride deposition. (© 2016 The Authors. Phys. Status Solidi RRL published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature-dependent photoluminescence of arsenic-doped Si nanocrystals

The characteristics of temperature-dependent photoluminescence (PL) from Si nanocrystals and effects of arsenic-doping (As-doping) were investigated. The Si nanocrystals on a p-type Si substrate were prepared by low pressure chemical vapor deposition and post-deposition thermal oxidation. The As-doping process was carried out using the gas-phase-doping technique. Temperature-dependent PL from Si nanocrystals exhibited considerable differences between samples with/without As-doping. Phase transition between electron-hole liquid and free exciton was observed in the undoped Si nanocrystals, leading to the increase in PL intensity with temperature less than 50 K. Electron emission from As-doped Si nanocrystals to the p-Si substrate was responsible for the significant increase in PL intensity with temperature greater than 50 K. Characteristics of light emission from Si nanocrystals will facilitate the development of silicon-based nanoscaled light-emitting devices.