A. Laugier

Defect-state generation in Czochralski-grown (100) silicon rapidly annealed with incoherent light

Defect‐state generation in Czochralski‐grown (100) silicon after rapid thermal annealing has been studied. Deep‐level transient spectroscopy experiments have been carried out using Schottky barriers made on n‐ or p‐type as‐grown wafers after irradiation with a commercially available incoherent light annealing device. Neither electrical degradation nor electron‐trap generation appeared in the case of n‐type silicon wafers annealed for 5 s. On the other hand, the junction degradation together with the generation of three hole‐trap levels H1(0.45 eV), H2(0.29 eV), and H3(0.3 eV) have been observed in boron‐doped silicon using a short duration (5 s) plateau temperature between 850 and 1050 °C. Peak concentrations ranging from 1013 to 1014 cm−3 were measured after annealing at 1000 °C for the three hole traps. By increasing the plateau duration up to 20 s hole traps were no longer detected in boron‐doped Czochralski‐grown silicon. Moreover H2(0.29 eV) is stable at room temperature whereas both H1(0.45 eV) and ...

Evaluation of quantum efficiency of porous silicon photoluminescence

The influence of photoluminescence of top porous silicon layer on deep p-n junction photocurrent is studied. The measurement of additional photocurrent caused by adsorption of porous silicon emission is shown to allow evaluation of the external quantum efficiency of photoluminescence. This can reach approximately 4% on n-Si upon illumination by the short wavelength tail of air mass (AM) 1.5 spectra.

Effect of rapid thermal processing on the intragrain properties of polysilicon as deduced from LBIC analysis

Abstract A high performance light-beam-induced-current (LBIC) analyser has been used to determine the influence of rapid thermal annealing (RTA) on the minority-carrier diffusion length ( L ). For this purpose a Schottky diode (Cr/Si) was fabricated on polycrystalline p-type silicon. The contacts were obtained by a “cold” technology. The diffusion length was determined by a laser spot scanning method. Present investigations on the effect of RTA on the intragrain transport properties showed a sharp decrease, and consequently a degradation in the overall solar cell efficiency, in L for samples subjected to RTA above 800°C; the smallest decrease in L after RTA above this temperature was more than two times the original L value of the unannealed sample. The evolution of L during some solar cell fabrication heat process treatments is also reported.

Transmission electron microscopy and EDS analysis of screen-printed contacts formation on multicrystalline silicon solar cells

In photovoltaic industry, contacts fabrication is an important step for solar cell efficiency improvement. In order to reduce the cost of the device, the metallizations are realized by screen-printing a paste. In this work, we have analyzed large area industrial solar cells with pn+ junction, SiO2 passivation layer and TiO2 antireflection coating (ARC) on front side. During the process, front contacts are screen-printed after TiO2 ARC deposition. The metallization paste is composed of a glass powder, an active metal (Ag for front paste and Ag/Al for rear paste) and a binding agent. Its deposition is followed by a rapid firing step at high temperature (firing through the oxide layers) and an annealing at lower temperature under reducing ambient. The aim of this study is to understand chemical and metallurgical mechanisms that occur in front and backside metallizations during heat treatments necessary for contacts formation. Cross-section samples are realized by the tripod method. Observations are realized with a 200 kV field effect gun-transmission electron microscope (TEM) associated to an EDS analysis. A software allows to pilot the beam, scanning along a surface or a line to obtain, respectively, an X-ray cartography or concentration profiles by elements. The main result of this analysis is that front contact ohmicity is not realized by the silver active metal of the paste but by metallic species coming from glass oxides.

SiGe Thin-Film Structures for Solar Cells

In order to study their applicability as the active base material in Si thin crystalline film solar cell technology, SiGe relaxed layers grown by Liquid Phase Epitaxy (LPE) and Chemical Vapor Deposition (CVD) on Si substrates are investigated by optical and electrical measurements (TEM, EXD, PL, EBIC). The main results of this work is to point out the improvement of the SiGe active base layer by using smooth Ge graded SiGe buffer layer and remote plasma hydrogenation. TEM, EXD, PL experiments show the effect of the Ge graded buffer layer grown using LPE, by confining the threading dislocations in the SiGe buffer layer close to the Si/SiGe interface. EBIC measurements reveal low recombination activity of dislocations at 300 K providing the diffusion length exceeds the 15 {micro}m layer thickness. The enhanced luminescence of SiGe near bandgap indicates that remote plasma hydrogenation induces a decrease of the non-radiative recombination pathways due to dislocations on CVD layers where defect recombinations dominate as indicated by EBIC measurements. This study points out the importance of controlling relaxed SiGe layers with good minority carrier recombination quality as a key issue for the optimization of new SiGe/Si based solar cells.

CARRIER COMPENSATION INDUCED BY RAPID THERMAL ANNEALING IN UNDOPED INP

The region beneath the interface of an InGaAs layer grown onto an undoped InP substrate by molecular beam epitaxy was investigated before and after rapid thermal annealing. Capacitance‐voltage measurements revealed a depletion region in the underlying InP due to donor compensation that is mainly caused by the Fe‐related Ec−0.63 eV‐deep level observed by deep level transient spectroscopy.

A new encapsulation method of InP during post implantation annealing

Abstract This paper describes a new encapsulation method of the surface of InP during post implantation annealing with a 1 μm thick InGaAs layer grown by molecular beam epitaxy. Secondary ion mass spectrometry microanalysis shows that the InGaAs/InP interface remains very stable upon rapid thermal annealing. However, capacitance-voltage measurements on MIS Schottky diodes reveal a wide depletion region in the underlying InP due to donor compensation. The proposed process has been successfully integrated in our technology of InP MISFET.

Outdiffusion modelling of arsenic from As+ implanted crystalline p-type silicon during rapid thermal annealing

Abstract High temperature rapid thermal annealing (RTA) of arsenic implanted (100) p-type silicon in the 1000–1200°C temperature range over short annealing periods (7–12 s) showed significant As losses from the upper layers of the implanted samples. Arsenic outdiffusion was modelled by solving the one-dimensional Ficks equation with semi-infinite boundary conditions using a concentration and temperature dependent diffusion coefficient D ( C , T ) and assuming that the dopant outdiffusion through the surface was thermally activated. The arsenic diffusion was classically attributed to As + V 2− , As + V − and As + V 0 pairs with the related concentration dependent diffusion coefficients taken from the literature. We introduced a wide range of activation energies (for outdiffusion) in the theoretical model; however, a low and constant value (typically 0.15 eV) yeilded the closest agreement with the experimental data irrespective of the annealing and implantation conditions. Based on this observation and the surface characterization data, obtained from X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements, we propose the arsenic loss to be predominantly controlled by the slowest step of the thermal decomposition of a complex arsenic species present in the near-surface region of the implanted samples that is independent of the geometrical and chemical nature or As in the bulk.

Grain Boundary Characterization in Polysilicon by Light Beam Induced Current Topography and Image Processing

A high performance light-beam-induced-current (LBIC) analyser has been used to determine the recombination velocity at the grain boundary (S) and the minority-carrier diffusion length (L). For this purpose a Schottky diode (Cr/Si) was fabricated using a p-type silicon bicrystal (1Ω cm, Σ13 grain boundary). The contacts were obtained by a “cold” technology. The diffusion length, determined by the method proposed by Ioannou, was subsequently fitted into the model proposed by Marek to evaluate the recombination velocity by the curve-fitting of the experimental and theoretical photocurrent profiles. A value of S = 2.10 4 cm/s was thus obtained. The influence of the thin oxide layer at the Cr/Si interface is also discussed.

Photoluminescence and secondary‐ion mass spectrometry studies of rapid‐thermal‐annealed silicon coimplanted with phosphorus in GaAs

Coimplantation effects of phosphorus (P) are studied for Si‐implanted GaAs by photoluminescence and secondary‐ion mass spectrometry. P coimplantation decreases SiAs acceptor intensity. At high temperatures rapid thermal annealing causes As loss, which favors the formation of the SiAs‐VAs complex. Diffusion of Si towards the GaAs bulk is not caused by P coimplantation but rather by the presence of carbon.