N-type Samples Research Articles

Anneal induced transformations of defects in hadron irradiated Si wafers and Schottky diodes

In this research, the anneal induced transformations of radiation defects have been studied in n-type and p-type CZ and FZ Si samples, irradiated with relativistic protons (24GeV/c) and pions (300MeV/c) using particle fluences up to 3 × 1016cm−2. The temperature dependent carrier trapping lifetime (TDTL) spectroscopy method was combined with measurements of current deep level transient spectroscopy (DLTS) to trace the evolution of the prevailing radiation defects. The contactless TDTL technique has been shown to be preferential when the radiation induced trap density approaches or exceeds the dopant concentration and when it is necessary to avoid modification of a detector structure due to annealing processes at elevated temperatures. The deep level spectra were complementarily examined by using DLTS spectroscopy on Schottky diodes made of irradiated Si wafer fragments. The dominant radiation defects and their transform paths under isothermal and isochronal anneals have been revealed. A good agreement between the DLTS and TDTL spectra has been obtained.

Transport properties of Cu-doped bismuth selenide single crystals at high magnetic fields up to 60 Tesla: Shubnikov–de Haas oscillations and [formula omitted]-Berry phase

We report Shubnikov-de Haas (SdH) and Hall oscillations in Cu-doped high quality bismuth selenide single crystals. To increase the accuracy of Berry phase determination by means of the of the SdH oscillations phase analysis we present a study of n-type samples with bulk carrier density n∼1019−1020cm−3 at high magnetic field up to 60Tesla. In particular, Landau level fan diagram starting from the value of the Landau index N=4 was plotted. Thus, from our data we found π-Berry phase that directly indicates the Dirac nature of the carriers in three-dimensional topological insulator (3D TI) based on Cu-doped bismuth selenide. We argued that in our samples the magnetotransport is determined by a general group of carriers that exhibit quasi-two-dimensional (2D) behaviour and are characterized by topological π-Berry phase. Along with the main contribution to the conductivity the presence of a small group of bulk carriers was registered. For 3D-pocket Berry phase was identified as zero, which is a characteristic of trivial metallic states.

Modulated Photoluminescence Lifetime Measurement of Bifacial Solar Cells

The frequency response of photoluminescence (PL) emission in a semiconductor sample is influenced by the effective carrier lifetime. As it is easy to induce and capture PL in solar cells at different stages of processing, modulated PL poses as a versatile technique to track the progression of effective lifetime in silicon wafer solar cells in the production line. This paper demonstrates the application of modulated PL to extract the effective carrier lifetime in n-type silicon bifacial solar cell samples before and after metalization. For nonmetalized samples, good agreement is found in the lifetime curves generated by modulated PL and the more established microwave photoconductance decay technique. For single and double-side metalized samples, the deduced lifetime is also consistent with the implied open-circuit voltage obtained by steady-state PL imaging.

Decoupling recombination mechanisms and trap state localization in direct bandgap semiconductors using photoluminescence decay

In this work, we show that extraction of the true bulk lifetime from the biexponential decay that follows from low initial carrier density photoluminescence decay experiments is not generally possible, and introduce new models to enable extraction of the bulk lifetime in the case where the initial carrier density exceeds the doping level. From measurements with high initial carrier density, we establish quasi-equilibrium between localized and free carrier states and accurately measure the bulk lifetime. Using our new models, we measure the time constants associated with localization processes as well as nonradiative and radiative bulk recombination in our GaAs double heterostructures grown with molecular beam epitaxy from experiments with varied excitation strength providing initial carrier densities that range from around 1014 to 1017 cm–3. We demonstrate that this approach can be applied to lightly doped (1016 cm–3) materials where the strongest excitation yields initial carrier densities that exceed the doping level. In our n-type sample, we report lifetime values of (22.7 ± 0.1) ns for bulk recombination, (73 ± 1) ns for trap-capture, (51 ± 2) ns for trap-emission, and (63 ± 2) ns for trap-decay, with a low-level injection effective radiative efficiency of (27.5 ± 0.7)%. In our p-type sample, we report lifetime values of (78.9 ± 0.3) ns for bulk recombination, (77.5 ± 0.7) ns for trap-capture, (530 ± 10) ns for trap-emission, and (177 ± 4) ns for trap-decay, with a low-level injection effective radiative efficiency of (47.0 ± 0.8)%. In comparison with the long and short lifetimes extracted from the biexponential decay with weak excitation, the mean bulk lifetime measured with strong excitation was (33 ± 2)% and (53 ± 1)% longer than the short lifetime, and (68 ± 4)% and (103 ± 3)% shorter than the long lifetime in our n-type and p-type samples, respectively. In our n-type sample, the extracted low-level injection nonradiative lifetime was (33 ± 1) ns, and it was observed to remain constant with the injection level. In our p-type sample, the high-level injection nonradiative lifetime was measured to be (30 ± 30)% larger than the low-level injection nonradiative lifetime of (140 ± 2) ns.

Long-Term Stability of Aluminum Oxide Based Surface Passivation Schemes Under Illumination at Elevated Temperatures

The stability of passivation layers under the conditions of field application of solar modules is a crucial parameter. We have performed an experiment to test the stability of aluminum oxide based passivation schemes under halogen lamp illumination of 1 sun equivalent intensity at 75 °C. We compare aluminum oxide layers with atomic layer deposition and plasma-enhanced chemical vapor deposition with and without an amorphous silicon nitride capping layer. Different thermal treatments are performed to activate the passivation or simulate solar cell contact firing. All passivation schemes are tested on full four inch 1 Ω·cm p- and n-type float-zone silicon wafers. The quality and stability of the surface passivation are tested by means of repeated charge carrier lifetime measurements. No significant surface passivation degradation due to light-soaking is evident on capped samples for several hundred hours. N-type samples are demonstrated to maintain excellent passivation quality for at least 3700 h and only slight degradation of p-type samples is found.

Stability of effective lifetime of float-zone silicon wafers with AlOx surface passivation schemes under illumination at elevated temperature

For solar cell application, the stability of interface passivation quality to in-field conditions is crucial. We have performed an experiment to test the resilience of different aluminium oxide based passivation schemes to illumination at 75 °C. Different thermal treatments to activate the passivation and/or simulate contact firing were performed before light soaking. The experiment was performed on 1 Ωcm float-zone silicon of both p- and n-type doping. The study demonstrates that good passivation quality can be achieved both by atomic layer deposition and by PECVD and that addition of silicon nitride capping layers greatly enhances thermal stability. On p-type wafers a severe but temporary degradation of the electrical quality of the wafer bulk was observed during the first hours upon application of such capping layers. Besides this effect, reasonable temporal stability of the effective lifetime was observed for p-type samples while n-type samples featured excellent long-term stability.

Impacts of light illumination on monocrystalline silicon surfaces passivated by atomic layer deposited Al2O3 capped with plasma-enhanced chemical vapor deposited SiNx

In this work, we investigate the impact of light illumination on crystalline silicon surfaces passivated with inline atomic layer deposited aluminum oxide capped with plasma-enhanced chemical vapor deposited silicon nitride. It is found that, for dedicated n-type lifetime samples under illumination, there is no light induced degradation (LID) but enhanced passivation. The lifetime increase happened with a much faster speed compared to the lifetime decay during dark storage, resulting in the overall lifetime enhancement for actual field application scenarios (sunshine during the day and darkness during the night). In addition, it was found that the lifetime enhancement is spectrally dependent and mainly associated with the visible part of the solar spectrum. Hence, it has negligible impact for such interfaces applied on the rear of the solar cells, for example p-type aluminum local back surface field (Al-LBSF) cells.

Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range

GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type) on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction of dopants causes a decrease in transparency of GaN substrates in a broad spectral range which is attributed to absorption on free carriers (n-type samples) or dopant ionization (p-type samples). In the mid-infrared the transparency cut-off, which for a semi-insulating GaN is at ~7 µm due to an absorption on a second harmonic of optical phonons, shifts towards shorter wavelengths due to an absorption on free carriers up to ~1 µm at n ~ 1020 cm−3 doping level. Moreover, a semi-insulating GaN crystal shows good transparency in the 1–10 THz range, while for n-and p-type crystal, the transparency in this spectral region is significantly quenched below 1%. In addition, it is shown that in the visible spectral region n-type GaN substrates with a carrier concentration below 1018 cm−3 are highly transparent with the absorption coefficient below 3 cm−1 at 450 nm, a satisfactory condition for light emitting diodes and laser diodes operating in this spectral range.

Raman and AFM studies on nominally undoped, p- and n-type GaAsBi alloys

We study structural properties and surface formation of undoped, n- and p-type doped GaAsBi alloys with various bismuth compositions using Micro-Raman, Fourier Transform (FT) Raman, Photoluminescence (PL) and Atomic Force Microscopy (AFM) techniques. PL is used to determine the suitable excitation source for Raman measurements and evaluate the Raman spectroscopy results. Room temperature PL results reveal that the bandgap energy of GaAsBi decreases with increasing bismuth composition at a rate of 82meV/%Bi. In micro-Raman spectra recorded using 532 nm laser line, a peak at around 185 cm−1 and a broad peak located between 210 and 250 cm−1 are observed. The absence of these peaks in the Raman spectrum of low temperature (LT) growth GaAs indicates that those peaks are bismuth-induced vibrations. Besides, the forbidden transverse optical (TO) mode (269 cm−1) becomes more pronounced for the samples as bismuth composition increases. FT-Raman spectra taken by 1064 nm laser line of the n- and p- type samples exhibit different characteristics; while TO and longitudinal optical (LO) peaks (291 cm−1) are present in n-type sample as sharp vibrational peaks, a broad peak located at slightly lower wavenumber than TO mode appears and LO peak is suppressed. The ionised acceptor and free hole system respond incident electromagnetic field as plasma oscillations. Moreover, the amplitude of the plasma oscillations enhances with higher doping density. Therefore, the appearance of the broad peak in FT-Raman spectrum of p-type GaAsBi is explained with an LO-plasmon coupling (LOPC). As for n-type samples, free electrons are compensated by free holes in GaAsBi that originate from Bi-induced acceptor-like defects. Therefore, we do not observe the effects of plasma oscillations in FT-Raman spectrum. AFM results reveal that all samples have surface droplets, and the size of the droplets is not affected from doping density or doping type, but bismuth composition. The surface droplets are removed by a chemical process to investigate the effect of the droplets on Raman spectrum. Our results reveal that removing surface droplets does not change the characteristic of Raman spectrum, but enhances the Raman intensity due to the reflected light by droplets decreases, leading to more photons penetrate and scattered from inside the sample.

Absolute measurement of effective radiative-efficiency in GaAs grown with molecular-beam-epitaxy

In this work, we have decoupled the radiative and nonradiative contributions to recombination by developing analytical models to fit observed non-monoexponential photoluminescence decay and bulk-lifetime temperature-dependence, which has enabled absolute measurement of the effective radiative efficiency and characterization of the dominant defect in lightly doped GaAs samples grown using molecular-beam-epitaxy. The measured effective radiative efficiency values under low level injection conditions range from (88.9 ± 0.1)% and (81.2 ± 0.1)% at 77 K to (0.028 ± 0.001)% and (0.034 ± 0.001)% at 700 K, with 300 K values of (17.3 ± 0.1)% and (10.5 ± 0.1)% in the p-type and n-type samples, respectively. A common defect-signature is observed in the temperature-dependence of the nonradiative lifetime in samples of both doping types, and our measured parameters are consistent with characteristics previously measured for the EL2 defect using deep-level transient spectroscopy.

Synthesis of N-type semiconductor diamonds with sulfur, boron co-doping in FeNiMnCo-C system at high pressure and high temperature**Project supported by the National Natural Science Foundation of China (Grant No. 11604246), China Postdoctor Science Foundation (Grant No. 2016M592714), Professional Practice Demonstration Base for Professional Degree Graduate in Material Engineering of Henan Polytechnic University, China (Grant No. 2016YJD03), the Education Department of

A series of diamonds with boron and sulfur co-doping were synthesized in the FeNiMnCo-C system by temperature gradient growth (TGG) under high pressure and high temperature (HPHT). Because of differences in additives, the resulting diamond crystals were colorless, blue-black, or yellow. Their morphologies were slab, tower, or minaret-like. Analysis of the x-ray photoelectron spectra (XPS) of these diamonds shows the presence of B, S, and N in samples from which N was not eliminated. But only the B dopant was assuredly incorporated in the samples from which N was eliminated. Resistivity and Hall mobility were 8.510 Ω·cm and 760.870 cm2/V·s, respectively, for a P-type diamond sample from which nitrogen was eliminated. Correspondingly, resistivity and Hall mobility were 4.211×105 Ω·cm and 76.300 cm2/V·s for an N-type diamond sample from which nitrogen was not eliminated. Large N-type diamonds of type Ib with B–S doping were acquired.

Physical properties of the type-I clathrate phase Ba8−xEuxAuySi46−y

The effect of the substitution of rare–earth atoms for guest atoms on the low-temperature transport and magnetic properties is investigated for single-crystalline type–I clathrates with the nominal composition Ba8−xEuxAuySi46−y (x = 1.0, 1.68 and y = 4.77, 5.32). The Seebeck coefficient and Hall coefficient data show that a transition from n- to p-type conduction takes place with increasing Au content. The n-type sample presents a large maximum in the thermal conductivity due to the freezing of three phonon Umklapp scattering processes at low temperatures, whereas the maximum of thermal conductivity in the p-type sample is strongly reduced due to dominant phonon-electron scattering process. Both samples are metal–like and ferromagnetic, with Curie temperatures TC of 3.1 K and 10.0 K for x = 1.0 and 1.68, respectively. The magnetization measurement confirmed the Eu2+ state in both samples and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction model explains the FM-type of order in which the nearest-neighbor (NNN) and the next-nearest-neighbor (NN) interactions play a major role at x = 1.0 and 1.68, respectively.

An insight of p-type to n-type conductivity conversion in oxygen ion-implanted ultrananocrystalline diamond films by impedance spectroscopy

The impedance spectroscopy measurements were used to investigate the separated contributions of diamond grains and grain boundaries (GBs), giving an insight into p-type to n-type conductivity conversion in O+-implanted ultrananocrystalline diamond (UNCD) films. It is found that both diamond grains and GBs promote the conductivity in O+-implanted UNCD films, in which GBs make at least half contribution. The p-type conductivity in O+-implanted samples is a result of H-terminated diamond grains, while n-type conductive samples are closely correlated with O-terminated O+-implanted diamond grains and GBs in the films. The results also suggest that low resistance of GBs is preferable to obtain high mobility n-type conductive UNCD films.

Carrier type change induced by fluorine doping in spin-chain compound Ca3Co2O6

Temperature dependence of thermopower for Ca3Co2O6−xFx.

Effect of melt-spun powder additions on the thermoelectric properties of bismuth and antimony chalcogenides

We have studied the thermoelectric properties of p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.4Se0.6 solid solutions prepared by vacuum hot pressing of mixtures of powders differing in particle size composition. The powders were prepared by mechanically grinding ingots and by ultrarapid melt cooling (melt spinning). Fracture surfaces of samples were examined by scanning electron microscopy. The samples consisted of large, layered particles of the major component (up to hundreds of microns in size) and small flakes (a few to tens of microns in size) of the component prepared by melt spinning. The microstructure of the materials was examined under an optical microscope. On grain boundaries in the p-type materials, we observed telluriumbased eutectic precipitates in the form of a white phase. In some of the n-type samples, the Bi2Te2.4Se0.6 solid solution was found to undergo ordering, resulting in the formation of the ternary compound Bi2Te2Se. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the materials were measured in the temperature range 100–700 K. The addition of 40 wt % powder prepared by melt spinning to hot-pressed p-type samples was shown to have no effect on their thermoelectric figure of merit (ZT)max, which was 1.0 at 350 K. On the addition of 20 wt % powder prepared by melt spinning, we obtained (ZT)max = 1.1 at 550 K in a hot-pressed n-type sample.

Precipitation of Cu and Ni in n- and p-type Czochralski-grown silicon characterized by photoluminescence imaging

Photoluminescence (PL) images and micro-PL maps were taken on Cu- or Ni-doped monocrystalline silicon wafers, to investigate the distribution of the metal precipitates. Several n-type and p-type wafers were used in which Cu or Ni were introduced in the starting melt of the ingots and precipitated during the ingot cooling (as opposed to surface contamination). The micro-PL mapping allowed investigation of the metal precipitates with a higher spatial resolution. Markedly different precipitation patterns were observed in n- and p-type samples: in both Cu- and Ni-doped n-type samples, circular central regions and edge regions were observed. In these regions, particles were distributed randomly and homogeneously. In the p-type Cu-doped and Ni-doped samples, by contrast, the precipitates occurred in lines along <110> orientations. The difference in the precipitation behaviour in n- and p-type samples is conjectured to be caused by different concentrations of self-interstitials and vacancies remaining in the crystal during the ingot cooling: there are more vacancies in the n-type ingots but more interstitials in the p-type ingots. The dopant effects on the intrinsic point defect concentrations in silicon crystals and possible precipitation mechanisms are discussed based on the findings in this work and the literature.

Simultaneous ohmic contacts to p- and n-type 4H-SiC by phase segregation annealing of co-sputtered Pt-Ti

A new concept, Phase Segregation Annealing (PSA), was investigated for implementing simultaneous ohmic contacts (SOCs) to p- and n-type 4H-SiC. Test structures with selected ratio compositions of co-sputtered Pt:Ti contacts were fabricated in p-type 4H-SiC epitaxial layers having aluminum acceptor concentrations, Na = 2 × 1019, 7 × 1019, and 2.5 × 1020 cm−3, and a nitrogen doped n-type epitaxial layer having donor concentration, Nd = 7 × 1018 cm−3. The ratios of the co-sputtered Pt-Ti metallization were 80:20, 50:50, and 30:70 at. %. After rapid thermal annealing (RTA) ranging between 800 and 1200 °C in vacuum and confirming SOCs by linear current-voltage (I-V) measurement, the specific contact resistance (ρc) values were extracted using the Transfer Length Measurement method. SOCs were realized with the Pt80:Ti20 composition starting from 1000 °C, and the Pt30:Ti70 composition from 1100 °C, with both exhibiting eutectic and segregated phases. The Pt50:Ti50 composition produced no SOC and eutectic and segregated phases were absent. The Pt80:Ti20 composition had the lowest pair of average ρc values of 7 × 10−5 Ω cm2 and 7.3 × 10−4 Ω cm2 on the highest doped p-type and the n-type samples after RTA at 1000 °C, respectively. Auger electron spectroscopy and focused ion beam field emission scanning electron microscopy with energy dispersive x-ray spectroscopy indicated distinct phase segregation via the eutectic-liquidus-eutectic transitions, the coalescence of likely Pt3Si and Pt2Si binary phases, and solid phases of Ti3Si, Ti5Si3, and TiC, with all the active phases maintaining intimate contact to both the p- and n-type 4H-SiC surfaces. The SOC formation was attributed to the disparate work functions of these phases, which was in good agreement with the proposed PSA model.

Fabrication of 200 mm Diameter Sintering Body of Skutterudite Thermoelectric Material by Spark Plasma Sintering

Filled skutterudite is a promising material for thermoelectric power generation because its ZT value is relatively high. However, mass production of high-performance thermoelectric materials remains a challenge. This study focused on the sintering process of thermoelectric materials. Large-diameter n-type (Yb or La, Ca, Al, Ga, In)0.8(Co, Fe)4Sb12 skutterudite sintering bodies with a small thickness were successfully produced by the spark plasma sintering (SPS) method. When direct current flows through the thermoelectric sintering body during the SPS pulse, the Peltier effect causes a temperature difference within the sintering body. To eliminate the Peltier effect, an electrical insulating material was inserted between the punch (electrode) and the sintering body. In this way, an n-type La-filled skutterudite sample with a diameter of 200 mm, thickness of 21 mm, and weight of 5 kg was successfully produced. The thermoelectric properties and microstructures of the sample were almost the same throughout the whole sintering body, and the dimensionless figure of merit reached 1.0 at 773 K.

Activation energy of negative fixed charges in thermal ALD Al2O3

A study of the thermally activated negative fixed charges Qtot and the interface trap densities Dit at the interface between Si and thermal atomic-layer-deposited amorphous Al2O3 layers is presented. The thermal activation of Qtot and Dit was conducted at annealing temperatures between 220 °C and 500 °C for durations between 3 s and 38 h. The temperature-induced differences in Qtot and Dit were measured using the characterization method called corona oxide characterization of semiconductors. Their time dependency were fitted using stretched exponential functions, yielding activation energies of EA = (2.2 ± 0.2) eV and EA = (2.3 ± 0.7) eV for Qtot and Dit, respectively. For annealing temperatures from 350 °C to 500 °C, the changes in Qtot and Dit were similar for both p- and n-type doped Si samples. In contrast, at 220 °C the charging process was enhanced for p-type samples. Based on the observations described in this contribution, a charging model leading to Qtot based on an electron hopping process between the silicon and Al2O3 through defects is proposed.

Long-term Stability of Al2O3 Passivated Black Silicon

In this work we report on the long-term stability of black silicon surfaces passivated with atomic layer deposited (ALD) 20nm thick Al2O3 films on p- and n-type FZ c-Si substrates. The results are directly compared with random pyramid textured counterparts. The effective surface recombination velocity Seff has been measured within a time frame of one year after activation of surface passivation. The results demonstrate that after an initial slight degradation during the first month Seff values stabilize around 45 and 25cm/s on p- and n-type black silicon samples, respectively. These values are enough to guarantee stable high efficiency in interdigitated back-contacted (IBC) c-Si(n) solar cells (> 24.5%) using black silicon nanostructures on the front side. Similar, although weaker, losses are also observed in surface passivation on textured samples covered by Al2O3 with equal thickness, indicating that the origin of the instability might be independent of surface morphology.