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Passivation capping that enhances the photoluminescence (PL) of molecular beam epitaxy (MBE)-grown InAs surface quantum dots (SQDs) is realized by ex situ low-temperature atomic layer deposition (ALD)-grown Al2O3. As the Al2O3 cap thickness increased from 2 to 30 nm, the PL intensity was enhanced by 2.7-fold and the blue shift was suppressed. This is in strong contrast to wet chemistry passivation and in situ GaAs capping by MBE, both of which resulted in significant PL blueshift, due to etching in the former, and In/Ga intermixing and strain in the latter. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the Al2O3 cap layer mimics the shape of the underlying SQDs. The cross-sectional transmission electron microscopy (TEM) further reveals that the SQD size and shape remained unchanged after Al2O3 capping, which is in strong contrast to MBE-capping. The passivation mechanisms and native oxide reduction by trimethylaluminum (TMA), including self-clean-up reaction through ligand exchange, are discussed based on the results by x-ray photoelectron spectroscopy (XPS). A detailed comparison between Al2O3 and ZnO cap layers reveals the significance of the cap properties on the SQD size/shape and PL blueshift. While the size/shape of SQDs is preserved by Al2O3 capping, the apex is slightly removed by ZnO capping, resulting in a stronger PL blueshift compared to Al2O3.

This paper proposes a new double carrier pulse deep-level transient spectroscopy (DC-DLTS) method that is applicable for evaluating metal–insulator–semiconductor (MIS) structures and the recombination centers in carrier-selective contact solar cells. Specifically, this study evaluated recombination characteristics of defects induced in bulk Si near SiO2/Si interfaces by reactive plasma deposition (RPD). In this method, a pulse voltage was first applied to inject majority carriers. Subsequently, a second pulse voltage was applied, which allowed minority carriers to be injected into the MIS structure. With these two types of carrier injections, carriers were recombined in recombination-active defects, and the DC-DLTS spectrum changed. During the injection of minority carriers, some majority carriers were thermally emitted from the defects, resulting in a decrease in the signal intensity. The recombination activity was analyzed by considering the effect of thermal emission on the change in signal intensity. The number of induced defect types and defect properties were estimated using Bayesian optimization. According to the results, three types of electron traps were generated using the RPD process. Based on the DC-DLTS results, defects with energy level 0.57 eV below the conduction band and capture cross section of ∼10−15 cm2 act as recombination centers.

The temperature dependence of electron spin resonance (ESR) has been measured to clarify the origin and nature of paramagnetic states responsible for the observed ESR signal in P+-implanted C60 films. Also, the temperature dependence of electrical conductivity was made and compared with ESR linewidths to detect the transport mechanism in these films. The ESR experiments were performed at 9.4 GHz in a wide temperature range from 3.7 to 300 K. The temperature dependence of the ESR signal intensity and spin susceptibility revealed that the unpaired spin follows the Curie law at T 20 K. The Curie behavior of the spin susceptibility results from localized dangling bond electrons, while a deviation occurs due to delocalization and excitation of electrons into states as the temperature increases. The temperature dependence of linewidths indicates that the spin mobility occurs by hopping, taking into account that the electron–phonon interaction as spin relaxation me...

The structure of the B and O related defect complex in Czochralski (CZ)-grown Si crystal is theoretically studied by using ab initio calculations. When a B-doped CZ Si wafer is used as a solar cell material, light irradiation and/or minority carrier injection causes the solar cell conversion efficiency to be degraded. Because the interstitial B and O complex is considered to be the key defect causing the degradation, the stable position of interstitial B in O-doped Si crystal is determined by ab initio calculations using the Si29B1O1H36 cluster system. Although interstitial B cannot directly create a stable chemical bond with interstitial O, it is found to exist stably as an interstitial B–substitutional Si–interstitial O complex. The interstitial B and substitutional Si atoms in the defect are positively charged and generate a deep energy level, indicating that this complex efficiently attracts an electron due to its electrical force and that it might act as a recombination center. When this complex is g...

Workfunction of reactive-plasma deposited indium-tin-oxide (RPD-ITO) at the ITO/SiO2 interface, which is referred as interface workfunction, and the process-induced damage are experimentally extracted for the first time based on capacitance-voltage (C-V) analysis. The estimated interface workfunction value of 4.74 eV for as-deposition condition is about 0.4 eV higher than that in the bulk determined by ultraviolet photoelectron spectroscopy (UPS). The RPD process induces the damage at the Si/SiO2 interface, and the degree of the damage is evaluated as the interface defect density (Dit) to be around 1012 cm-2eV-1. The effects of forming-gas annealing on the interface workfunction and recovery of the damage are also studied. The interface workfunction value once decreases to 4.53 eV by the annealing up to 250 oC and then turns to increase to 4.77 eV after 400 oC annealing. The damage is annihilated by the low-temperature forming-gas annealing at 200 oC.

The effects of residual C on cell properties are investigated from the view point of thermal budget in the n-type bifacial cell processes. Implied Voc obtained from wafers with same Oi concentration depend on the thermal budgets decreases as the Cs concentration increases. The Voc values vary depending on the wafer with different growth cooling rate. To analyze the effect of thermal budget correspond to solar cell fabrication process, CZ wafers with almost the same Oi concentrations are prepared. One of the wafers with relatively high residual Cs concentration shows the longer lifetime than the initial value after the 950 oC annealing step. On the other hand, the lifetime of a wafer with relatively low Cs concentration dramatically decreased by the same process due to the O segregation. These results suggest that it is important to choose appropriate wafer specification, starting with feedstock material, for increasing the solar cell efficiency.

The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect EV+0.36 eV has been identified as Ci–Oi complexes. The absence of an EC−0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the Bi–Oi complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level EV+0.36 eV (Ci–Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC−0.18 eV (Bi–Oi). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level EV+0.18 eV in gallium-doped samples at around 350 °C, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si.

Conductivity control of the boron and phosphorus ion implanted C60 films subjected to various doses with multiple energy has been investigated. Temperature dependent conductivity shows the semiconducting nature of the B+ and P+ implanted films. Fourier transform infrared spectra of the B+ and P+ implanted C60 films show the structural change of the C60 into amorphous carbon. Optical gaps of the implanted films have been observed as a function of implantation dose. The dramatic increase in the conductivity and the reduction in the optical gap on ion implantation are thought to be attributed to an increase in sp2 bounded states, lattice damage, and substitutional impurity doping with ion implantation. The B+ and P+ implantation into C60 and amorphous carbon suggests the possibility of fabricating carbon based homojunction solar cells.

The adhesive energies at Cu/SiO2, Cu/TiN, and Cu/TiW interfaces were investigated by measuring the contact angles of Cu particles to the substrate. To form the Cu particles, thin Cu films deposited on each substrate were annealed at 500 °C for 50 h. The adhesive energies are determined to be 0.8, 1.8, and 2.2 N/m for the SiO2, TiN, and TiW, respectively. The Cu particle on TiW film shows the highest adhesion. When TiW is used as a barrier metal, fine Cu lines are fabricated by reactive ions etching without peeling. On the other hand, Cu lines on the TiN film are peeled during the etching. This is consistent to the evaluation result that TiW has higher adhesive energy than TiN.

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

The details of the process of carrier recombination via the Shockley-Read-Hall (SRH) defect level, at the grain boundaries of multicrystalline silicon, were investigated. For this, the temperature-dependent recombination velocities, as determined by experiments, were analyzed by the application of an electron beam induced current method. For the model, the misorientation angles at the grain boundaries were defined using a multi-seed casting-growth method. The results of our experiments indicated different temperature behaviors at low and high temperatures. These can be explained by controlling the process anticipated by the SRH model, that is, the process whereby minority carriers (electrons) are captured at lower temperatures, followed by the reemission of the carriers before recombination with Arrhenius behavior at higher temperatures. The minority capture process appeared to conform to the power law T−α temperature behavior. Thus, there are two candidate electron capture mechanisms, namely, cascade pho...

To keep the current density at the porous silicon (PS) and Si interface constant, independent of anodization depth, a pulse anodization method has been developed. In this method, a pulse current is controlled to be proportional to the PS/Si interface area. This method was applied to produce two-layered PS with different pore sizes. Titanium organic molecules were selectively doped into larger sized pores. By oxidization, the PS was transformed into a densified silica waveguide and its core, and cladding was automatically formed, without significant volume change. Very few breaking defects have been found in the waveguides. In addition, bends in the Si substrates were small. Optical loss in the slab waveguides was 0.3 dB/cm at 632.8 nm.

Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures.

The incorporation of Si in GaAsN alloys grown simultaneously on (100), (311)A, (311)B, and (211)B GaAs substrates by the chemical beam epitaxy has been investigated. The decrease in electron concentration with the increasing N composition suggests the occurrence of N and Si interaction, whereas the interaction exhibits evidently different extent depending on the growth orientation. Combined with the secondary ion mass spectrometry and photoluminescence measurements, it is revealed that (311)B and (211)B are the promising substrate orientations to reduce the N-Si passivation and improve n-type Si doping in GaAsN over a wider N composition range. A surface bonding model is utilized to explain the plane polarity dependent incorporation behaviors of Si and N.

The hole traps associated with high background doping in p-type GaAsN grown by chemical beam epitaxy are studied based on the changes of carrier concentration, junction capacitance, and hole traps properties due to the annealing. The carrier concentration was increased dramatically with annealing time, based on capacitance–voltage (C–V) measurement. In addition, the temperature dependence of the junction capacitance (C–T) was increased rapidly two times. Such behavior is explained by the thermal ionization of two acceptor states. These acceptors are the main cause of high background doping in the film, since the estimated carrier concentration from C–T results explains the measured carrier concentration at room temperature using C–V method. The acceptor states became shallower after annealing, and hence their structures are thermally unstable. Deep level transient spectroscopy (DLTS) showed that the HC2 hole trap was composed of two signals, labeled HC21 and HC22. These defects correspond to the acceptor levels, as their energy levels obtained from DLTS are similar to those deduced from C–T. The capture cross sections of HC21 and HC22 are larger than those of single acceptors. In addition, their energy levels and capture cross sections change in the same way due to the annealing. This tendency suggests that HC21 and HC22 signals originate from the same defect which acts as a double acceptor.

The in situ heavy phosphorus doping effects on polycrystalline‐silicon selective deposition were studied using the SiH2Cl2/H2/PH3/HCl/gas system. By increasing the PH3 flow rate, the growth rate was drastically decreased and selectivity was improved. The results indicated that the growth rate was determined by the impurity surface coverage. The correlation between the growth rate and the PH3 flow rate was well explained by Frumkin–Temkin type adsorption model.

β‐SiC is grown on a silicon substrate by the chemical vapor deposition method using the SiH2Cl2/i‐C4H10/H2/HCl gas system. Stoichiometric β‐SiC films are obtained with high growth rate at a low temperature of 900 °C. Highly (111) oriented β‐SiC polycrystal is grown on a Si(111) substrate. Moreover, using the above‐mentioned gas system, β‐SiC selective growth is attained on a Si substrate, with no nucleation on the SiO2 area. This letter discusses the i‐C4H10 effects and selective growth condition.

Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through in situ x-ray reciprocal space mapping (in situ RSM). At the synchrotron radiation facility SPring-8, a hybrid system of molecular beam epitaxy and x-ray diffractometry with a two-dimensional detector enabled us to perform in situ RSM at high-speed and high-resolution. Using this experimental setup, four results in terms of film properties were simultaneously extracted as functions of film thickness. These were the lattice constants, the diffraction broadenings along in-plane and out-of-plane directions, and the diffuse scattering. Based on correlations among these results, the strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In addition, the existence of transition regimes between the thickness ranges was identified. Finally, the dominant dislocation behavior corresponding to each of the four thickness ranges and transition regimes was noted.

Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In0.12Ga0.88As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [1¯10] directions caused by α and β misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by α-MDs is higher than that caused by β-MDs, and therefore crystal quality along [110] is worse than that along [1¯10]. Rapid relaxation along both [110] and [1¯10] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [1¯10] direction, presumably due to β-MDs, becomes better that along [110] direction and the ratio does not decay with thickness.

A simple fabrication technique for subwavelength structured (SWS) surfaces by means of anodic porous alumina masks directly formed on Si substrates was proposed and demonstrated. By this technique, SWS surfaces were fabricated on polished single-crystalline Si and chemically etched as-cut multicrystalline Si wafers. Smoothly tapered SWS surfaces with a periodicity of 100nm and a height of 300–400nm were obtained. A low reflectivity below 1% was observed from 300to1000nm for both of the wafers, in agreement with numerical simulation. After thermal annealing at 800°C, the reflectivity of the SWS surface increased to 3%.

UV light irradiation effects on prebaking and silicon epitaxial growth is studied. An ArF excimer laser, a KrF excimer laser, and a Hg‐Xe lamp are used as light sources. The epitaxial growth is carried out using a SiH2Cl2/H2 system under reduced pressure. ArF radiation and Hg‐Xe radiation are found to be effective for volatilizing native SiO2 on silicon‐substrate surfaces even at low temperatures. When a substrate surface is irradiated with these UV radiations during prebaking and epitaxial growth, epilayer surface morphology and crystalline quality are much improved. Furthermore, the epitaxial growth rate seems to be enhanced photothermally by excimer laser radiations, and photochemically by Hg‐Xe radiation.

Triethylgallium (TEG) adsorption on Si(100) 2×1 and Si(111) 7×7 surfaces was studied by reflection high‐energy electron diffraction (RHEED) and x‐ray photoelectron spectroscopy (XPS). At room temperature, TEG molecules nondissociatively adsorbed on Si surface. Being judged from the Ga 2P3/2 and C 1s peak height, TEG molecules dissociatively adsorbed and Ga was selectively deposited on Si surfaces at temperatures between 200 and 500 °C. At temperatures above 500 °C, Ga thermal desorption was observed. RHEED pattern showed the β‐SiC growth in this temperature range. Temperature dependence of the Ga 2P3/2 peak at Si(100) was different from that at Si(111), which strongly suggests that the surface dangling bond plays an important role in TEG dissociative adsorption.