P-type Wafers Research Articles

Selective growth of single-crystalline ZnO nanowires on doped silicon

We report the growth of single-crystalline ZnO nanowires on n- and p-type Si wafers by electrodeposition. On strongly doped n-type Si high-quality nanowires can be grown under similar conditions as used for metallic substrates. For low electron concentrations occurring in weakly n-type or in p-type wafers, nanowire growth is inhibited. This difference allows selective growth in strongly n-type areas. The inhibited growth on weakly n-type and p-type wafers can be improved by applying stronger cathodic electrode potentials or by illuminating the growth area. The wires on n-Si show efficient electroluminescence covering the visible and extending into the ultraviolet spectral range.

Electrical passivation by hydrogen of substitutional cobalt in monocrystalline germanium

Co has been implanted at 90 keV in n- and p-type germanium wafers and in-diffused using a 5 min thermal anneal at 500 ∘ C . Deep level transient spectroscopy reveals three levels which are considered to be due to substitutional Co impurities. To passivate the electrical levels of substitutional Co, samples were hydrogenated using a DC-plasma for 4 h at 200 ∘ C . For both the n- and p-type material the Co levels have disappeared up to at least 5 μ m beyond the surface. Directly after the plasma treatment different levels due to irradiation damage have been observed, one of which was assigned to the di-vacancy. The irradiation damage related defects disappeared due to a rapid thermal anneal of 1 min at 400 ∘ C . Two electron traps E230 and E270 which were only present in Co-implanted samples after a hydrogenation have been tentatively assigned to cobalt related defect levels.

Deep level transient spectroscopy of transition metal impurities in germanium

The n- and p-type germanium wafers have been implanted with Ti, Cr, Fe and Co and the electronic defect levels have been studied by deep level transient spectroscopy (DLTS). Distinct spectra with two to four levels have been observed which are assigned to multiple-acceptor states of the substitutional metal impurities, with, in addition, a deep donor level in the case of Cr and Co. Thermally activated capture cross-sections are observed for the electron traps, in agreement with this assignment. For Fe and Co the DLTS results confirm earlier Hall-effect data, while for Ti and Cr a reliable deep level spectrum has been obtained for the first time.

Modification of the properties of porous silicon on adsorption of iodine molecules

Infrared spectroscopy and electron spin resonance measurements are used to study the properties of porous silicon layers on adsorption of the I2 iodine molecules. The layers are formed on the p-an n-Si single-crystal wafers. It is established that, in the atmosphere of I2 molecules, the charge-carrier concentration in the layers produced on the p-type wafers can be noticeably increased: the concentration of holes can attain values on the order of ∼1018−1019 cm−3. In porous silicon layers formed on the n-type wafers, the adsorption-induced inversion of the type of charge carriers and the partial substitution of silicon-hydrogen bonds by silicon-iodine bonds are observed. A decrease in the concentration of surface paramagnetic defects, P b centers, is observed in the samples with adsorbed iodine. The experimental data are interpreted in the context of the model in which it is assumed that both deep and shallow acceptor states are formed at the surface of silicon nanocrystals upon the adsorption of I2 molecules.

First-principles analysis of interfacial nanoscaled oxide layers of bonded N- and P-type GaAs wafers

First-principles analysis is applied in relating microstructures with properties of interfacial nanoscaled oxide layers of bonded N- and P-type GaAs wafers. Using high-resolution transmission electron microscope results, the detailed atomic arrangements of materials specimen can be obtained and fed into the first-principles calculations. Therefore, the corresponding electronic structure and associated property can be reliably derived to identify responsible microstructural features. The electrical performance is found to be closely related to the variation of nanosized interface morphology and types of wafers.

Porous silicon microcavities fabricated using ion irradiation

By employing microcavity (MC) techniques, the broad spectral band and wide emission angle of photoluminescence from porous silicon (PSi) can be narrowed, directed and tuned in PSi microcavities. The microcavity structure is formed with a porous silicon active layer sandwiched between two Bragg reflectors. We have characterised the optical properties of the porous silicon multilayer structures. A number of Bragg reflectors and Fabry–Perot optical microcavities are fabricated with tuning of emission wavelengths over a wide range in heavily doped p-type silicon. The optical properties of these microstructures were investigated using reflectivity and photoluminescence measurements at different temperatures. This paper reports the ability of focussed 2 MeV proton beam irradiation to controllably blue shift the resonant wavelength of porous silicon microcavities in heavily doped p-type wafers. Using this process wafers are patterned on a micrometer lateral scale with microcavities tuned to different resonant wavelengths, giving rise to high-resolution full-colour reflection images over the full visible spectrum.

Cobalt related defect levels in silicon analyzed by temperature- and injection-dependent lifetime spectroscopy

Temperature- and injection-dependent lifetime spectroscopy (TIDLS) as a method to characterize point defects in silicon with several energy levels is demonstrated. An intentionally cobalt-contaminated p-type wafer was investigated by means of lifetime measurements performed at different temperatures up to 151°C. Two defect energy levels were required to model the lifetime curves on basis of the Shockley-Read-Hall statistics. The detailed analysis is based on the determination of the recently introduced defect parameter solution surface (DPSS) in order to extract the underlying defect parameters. A unique solution has been found for a deep defect level located in the upper band gap half with an energy depth of EC−Et=0.38±0.01eV, with a corresponding ratio of capture cross sections k=σn∕σp=0.16 within the interval of uncertainty of 0.06–0.69. Additionally, a deep donor level in the lower band gap half known from the literature could be assigned to a second energy level within the DPSS analysis at Et−EV=0.41...

Photoresponse of hydrogen plasma treated and electron irradiated silicon wafers

Photovoltage (PV) spectra of standard commercial Czochralski n- and p-type silicon wafers with different resistivity subjected to hydrogenation and/or 3.5 MeV electron irradiation have been studied. The PV signal was generated using a band bending present in the wafers. For more information about the influence of hydrogenation and/or electron irradiation on the wafer properties, the measurements of thermo-EMF and surface resistance have been made. The experiments have shown that the hydrogenation of the p-type wafers leads to the appearance of PV signal similar to that for silicon photodiodes as a result of the n-type layer creation near the hydrogenated surface. A drawing field created in the p-type wafers in consequence of their hydrogenation decreases the effect of the carrier diffusion length reduction due to electron irradiation that makes the hydrogenated p-type wafers less sensitive to the radiation impact.

Effect of hydrogen implantation on semiconductor–metal transition and high-pressure thermopower in Si

In the present work Czochralski-grown silicon single crystals were investigated implanted with different doses of H + ions. The Si wafers were characterized by the Raman scattering technique. Thermoelectric power was studied in a pressure range of 0–20 GPa of p-type Si single crystal wafers containing a thin hydrogenated layer consisting of amorphous Si, nanocrystalline Si and H-rich Si layers. In the region of the pressure-induced phase transition from the initial semiconductor diamond-like into the metal β-Sn lattice, a lowering of thermopower values was noticed in comparison with ones of p-Si.

Laser annealing for n +/p junction formation in germanium

In the present work we focus our study on laser annealing of implanted with high phosphorus dose p-type germanium wafers using an Nd-YAG laser at 355 nm. Dopant profiles as monitored by SIMS measurements demonstrate dopant profile movement less than 15 nm at junction depth. Germanium (Ge) structural defects were observed by TEM measurements and the roughness of the surface was measured by AFM. The above analysis shows the efficiency of laser annealing in recrystallizing the Ge substrates at lower energy fluences compared to Si and without substantial dopant loss and diffusion.

Minority-carrier trapping in Ga-doped multicrystalline Si wafers

Abstract B- and Ga-doped multicrystalline-silicon (mc-Si) wafers with different resistivity and different positions of grown ingots have been used to evaluate the stability, quality improvement and thermal annealing effects on carrier lifetimes. The effective carrier lifetimes are improved and high lifetimes as high as 200 μs are realized after P-diffusion and SiN x coating. Ga-doped wafers show a certain stability after thermal annealing up to 250 °C which insures the possibilities of eliminating the light-induced degradation effects generated in p-type mc-Si wafers.

Controlled blueshift of the resonant wavelength in porous silicon microcavities using ion irradiation

High-energy focused proton beam irradiation has been used to controllably blueshift the resonant wavelength of porous silicon microcavities in heavily doped p-type wafers. Irradiation results in an increased resistivity, hence a locally reduced rate of anodization. Irradiated regions are consequently thinner and of a higher refractive index than unirradiated regions, and the microcavity blueshift arises from a net reduction in the optical thickness of each porous layer. Using this process wafers are patterned on a micrometer lateral scale with microcavities tuned to different resonant wavelengths, giving rise to high-resolution full-color reflection images over the full visible spectrum.

Thermal donor generation in Czochralski silicon particle detectors

In this report, the processing of thermal donor (TD) compensated detectors is described. Heat treatment of Czochralski silicon (Cz-Si) wafers between 400 and 600 °C leads to aggregation of interstitial oxygen atoms resulting in electrically active shallow levels in the silicon band gap. This process is known as TD formation. It depends on the temperature, the oxygen concentration in the silicon material and the presence of hydrogen in device manufacturing process. The oxygen concentration in silicon wafers grown by Magnetic Czochralski (MCz) method is sufficiently high in order that the concentration of TDs is comparable with the initial phosphorous or boron doping of high-resistivity Cz-Si. The TD formation has been studied by monitoring the detector full depletion voltage with respect to the heating time at 430 °C. The TD formation has been verified by Deep Level Transient Spectroscopy (DLTS) measurements. In addition, the annealing behavior of the irradiated samples at different temperatures is discussed. The TD formation in n +/p −/p + pad detectors has been observed not to influence the leakage current of the devices. Thus, the full depletion voltage of the detectors processed on p-type MCz-Si wafers can be modified by this method.

Nanoscaled interfacial oxide layers of bonded n- and p-type GaAs wafers

This work examined in detail the electrical characteristics and microstructures of in- and antiphase bonded interfaces for both n- and p-type GaAs wafers treated at 500 and 600°C, respectively. The n-GaAs wafers did not bond directly to itself but instead via an amorphous oxide layer at 500°C. These temperatures are lower than most other works. The nonlinear behavior of the current versus the voltage is related to the potential barrier formed at the continuous oxide interface. Both experimental observation and first-principles calculations confirm the existence of this barrier. The higher interface energy for the antiphase bonding tends to stabilize the interfacial oxide layer. The evolution of interfacial layers occurred much faster for the p-type wafers than for n-type wafers. Electrical performance was found to be closely related to the variation of nanosized interface morphology.

Scanning techniques applied to the characterisation of P and N type multicrystalline silicon

Multicrystalline silicon wafers (mc-Si) are characterized by high densities of crystallographic defects and impurities like oxygen and heavy metals. Recombination centres are generated at grain boundaries and dislocations by segregated impurities and other centres are created in the grains by dissolved impurities. The electrical properties of mc-Si are inhomogeneous and their characterisation in terms of lifetime ( τ) and diffusion length ( L) of minority carriers requires application of mapping techniques. Maps are obtained by means of reflected microwave intensity, spectroscopic photoluminescence or light beam-induced current techniques. P-type mc-Si wafers were intensively investigated in the last years, but n-type was not, although it is of a particular interest. Indeed, the capture cross sections of metallic impurities are frequently smaller than those found in p-type and it is expected that L p are higher than L n. It is shown that the electrical properties of p-type wafers are well described by τ and L scan maps, which are well correlated with the features of defects. However, in as cut n-type wafers L values are so high that they are overestimated due to the lateral diffusion of photocarriers. Photoluminescence (PL) maps are well correlated with lifetime scan maps and they indicate that dislocation-related defects have low recombination activity, which is confirmed by negligible intensity of the room-temperature “defect” PL band with the maximum at 1,560 nm.

Study of optical properties of swift heavy ion irradiated gallium antimonide

Gallium antimonide (GaSb) which is a narrow band gap compound semiconductor has received attention because of its potential applications in optoelectronic devices. In the present work, p-type GaSb wafers of 〈100〉 orientation were irradiated with 70MeV 56Fe ions at fluences varying from 1×1012 to 1×1014 ions cm−2. Mid-infrared and Far-infrared Fourier Transform (FT) measurements were carried out to investigate the optical properties of as irradiated and vacuum annealed samples. Mid-infrared Fourier Transform study revealed that the optical absorption of the irradiated samples increases with increasing ion fluence due to increase in irradiation-induced defects. The band gap energy determined from the infrared spectra was found to change from 0.65 to 0.62eV while for non-irradiated GaSb wafer the corresponding estimate was 0.67eV. The density of the carrier estimated from the plasma frequency (ωp) was found to vary from 2.05×1018 to 1.9×1018cm−3. The samples annealed in vacuum (10−6mb) over the temperature range 100–600°C showed the significant damage recovery.

High-efficiency solar cells on phosphorus gettered multicrystalline silicon substrates

Measurements of the dislocation density are compared with locally resolved measurements of carrier lifetime for p-type multicrystalline silicon. A correlation between dislocation density and carrier recombination was found: high carrier lifetimes (>100 µs) were only measured in areas with low dislocation density ( 106 cm−2) relatively low lifetimes (<20 µs) were observed. In order to remove mobile impurities from the silicon, a phosphorus diffusion gettering process was applied. An increase of the carrier lifetime by about a factor of three was observed in lowly dislocated regions whereas in highly dislocated areas no gettering efficiency was observed. To test the effectiveness of the gettering in a solar cell manufacturing process, five different multicrystalline silicon materials from four manufacturers were phosphorus gettered. Base resistivity varied between 0·5 and 5 Ω cm for the boron- and gallium-doped p-type wafers which were used in this study. The high-efficiency solar cell structure, which has led to the highest conversion efficiencies of multicrystalline silicon solar cells to date, was used to fabricate numerous solar cells with aperture areas of 1 and 4 cm2. Efficiencies in the 20% range were achieved for all materials with an average value of 18%. Best efficiencies for 1 cm2 (20·3%) and 4 cm2 (19·8%) cells were achieved on 0·6 and 1·5 Ω cm, respectively. This proves that multicrystalline silicon of very different material specification can yield very high efficiencies if an appropriate cell process is applied. Copyright © 2006 John Wiley & Sons, Ltd.

P/sup +//n/sup -//n/sup +/ cz-Si detectors processed on p-type boron-doped substrates with thermal donor induced space charge sign inversion

We have processed pad detectors on high-resistivity p-type Cz-Si wafers. The resistivity of the boron-doped silicon is approximately 1.8 k/spl Omega/ cm after the crystal growth. The detector processing was carried out using the common procedure for standard n-type wafers, to produce p/sup +//p/p/sup -//n/sup +/ detector structures. During the last process step, i.e., sintering of aluminum electrode, the p-type bulk was turned to n-type through generation of thermal donors (TD). This way, high oxygen concentration p/sup +//n/sup -//n/sup +/ Cz-Si detectors were realized with low temperature process. The full depletion voltage of detectors could be tailored between wide range from 30 V up to close 1000 V by changing heat treatment at 400/spl deg/C-450/spl deg/C duration from 20 to 80 min. The space charge sign inversion (SCSI) in the TD generated devices (from p/sup +//p/sup -//n/sup +/ to p/sup +//n/sup -/(inverted)/n/sup +/) has been verified by transient current technique measurements. The detectors show very small increase of full depletion voltage after irradiations with 24 GeV/c protons up to 5*10/sup 14/ p/cm/sup 2/.

Effect of emitter deposition temperature on surface passivation in hot-wire chemical vapor deposited silicon heterojunction solar cells

Low substrate temperature (< 150 °C) during initiation of amorphous silicon emitter deposition by hot-wire chemical vapor deposition is found to be crucial for reaching high open-circuit voltage ( V oc) in an amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cell. Low-temperature results in immediate a-Si deposition and a smooth interface to the c-Si substrate. The smooth heterojunction leads to effective passivation of the c-Si surface by the a-Si intrinsic layer through a much-reduced interface recombination velocity, and V oc is consistently above 620 mV. We obtain a V oc above 640 mV and a fill factor of 80% on Al-backed p-type Czochralski wafers with emitters deposited at temperatures below 135 °C. Energy conversion efficiencies of 14.8% and 15.7% are obtained on a polished p-type Czochralski silicon wafer and a polished p-type float-zone silicon wafer, respectively.

Examination of Relationship Between Resistivity and Photocurrent Induced Magnetic Field in Silicon Wafers Using Laser SQUID

Using the laser SQUID method, we examined the relationship between silicon wafer resistivity and magnetic field. By irradiating the wafer with a 3.2 W high-power laser beam, we were able to generate a measurable magnetic field perpendicular to the wafer, even for the wafers without p-n junctions. For samples having resistivities of 130 /spl Omega//spl middot/cm or less, we observed magnetic field distributions in the form of concentric circles. Histogram analysis showed that as resistivity decreases, mean value of magnetic field and standard deviation increase. For p-type wafers having resistivities of up to 300 /spl Omega//spl middot/cm, both mean value of magnetic field and standard deviation vary as a power law with respect to resistivity. However, for samples having resistivities of 300 /spl Omega//spl middot/cm or higher, the relationship was saturated, and determining resistivity was difficult. Since the laser SQUID method can be used to measure resistivity without electrical contact, it works well even for wafers with surface oxide films, and does not cause contamination.