Carrier Concentration In Layer Research Articles

Free-charge carrier parameters of n-type, p-type and compensated InN:Mg determined by infrared spectroscopic ellipsometry

Infrared spectroscopic ellipsometry is applied to investigate the free-charge carrier properties of Mg-doped InN films. Two representative sets of In-polar InN grown by molecular beam epitaxy with Mg concentrations ranging from 1.2×1017cm−3 to 8×1020cm−3 are compared. P-type conductivity is indicated for the Mg concentration range of 1×1018cm−3 to 9×1019cm−3 from a systematic investigation of the longitudinal optical phonon plasmon broadening and the mobility parameter in dependence of the Mg concentration. A parameterized model that accounts for the phonon–plasmon coupling is applied to determine the free-charge carrier concentration and mobility parameters in the doped bulk InN layer as well as the GaN template and undoped InN buffer layer for each sample. The free-charge carrier properties in the second sample set are consistent with the results determined in a comprehensive analysis of the first sample set reported earlier [Schöche et al., J. Appl. Phys. 113, 013502 (2013)]. In the second set, two samples with Mg concentration of 2.3×1020cm−3 are identified as compensated n-type InN with very low electron concentrations which are suitable for further investigation of intrinsic material properties that are typically governed by high electron concentrations even in undoped InN. The compensated n-type InN samples can be clearly distinguished from the p-type conductive material of similar plasma frequencies by strongly reduced phonon plasmon broadening.

Photo-induced persistent inversion of germanium in a 200-nm-deep surface region.

The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.

Towards understanding the superfluid behavior in double layer graphene nanostructures

The unique electronic properties that are found in graphene layers have been touted as an attractive means to not only study fundamental physical principles but to design new types of electronic and optical information processing technologies. Of the physical observables present in graphene which may be exploited for device technologies, the proposed superfluid phase transition of indirectly bound excitons in closely spaced layers of graphene is one of the most exciting. Nevertheless, the superfluid phase of double layer graphene remains a poorly understood quantity. In this work, we theoretically investigate the properties of the superfluid phase in double layer graphene systems via two disparate methods: path-integral quantum Monte Carlo and non-equilibrium Green's functions. We show that the superfluid phase in double layer graphene persists up to ambient temperatures in spinless systems. When we increase the number of degrees of freedom in the system to include spin, we find that the screening effectiveness is suppressed by intralayer correlations resulting in higher transition temperatures than previously predicted. Furthermore, we estimate the magnitude of the interlayer currents that the superfluid can sustain under non-ideal conditions by considering the effects of layer disorder and the electron-phonon interaction. We show that the superfluid dynamics is significantly affected not only by the total amount of disorder but also depends very heavily on the location of the disorder in the layers. When the electron-phonon interaction is included, we demonstrate that for high layer carrier densities the electron-phonon interaction does not affect superfluid flow but degrades the transport properties significantly as the layer carrier concentration decreases.

Device characteristics of Ti–InSnO thin film transistors with modulated double and triple channel structures

The device characteristics of Ti–InSnO thin film transistors (TFTs) with modulated channels were investigated. The field effect mobility was enhanced to 14.9 cm2/Vs in the channel-modulated TFT. The electrical performance of the TFT device was improved by the insertion of a high carrier concentration layer at the channel/gate insulator and channel/electrode interfaces. It was due to the enhancement of carrier accumulation and the reduction of parasitic resistance via channel modulation. The threshold voltage was controlled at moderate value. These results indicate that the device characteristic of TFTs can be enhanced by the modulated channel structure.

Infrared to vacuum-ultraviolet ellipsometry and optical Hall-effect study of free-charge carrier parameters in Mg-doped InN

Infrared to vacuum-ultraviolet spectroscopic ellipsometry and far-infrared optical Hall-effect measurements are applied to conclude on successful p-type doping of InN films. A representative set of In-polar Mg-doped InN films with Mg concentrations ranging from 1.2×1016 cm−3 to 3.9×1021 cm−3 is investigated. The data are compared and discussed in dependence of the Mg concentration. Differences between n-type and p-type conducting samples are identified and explained. p-type conductivity in the Mg concentration range between 1.1×1018 cm−3 and 2.9×1019 cm−3 is indicated by the appearance of a dip structure in the infrared spectral region related to a loss in reflectivity of p-polarized light as a consequence of reduced LO phonon plasmon coupling, by vanishing free-charge carrier induced birefringence in the optical Hall-effect measurements, and by a sudden change in phonon-plasmon broadening behavior despite continuous change in the Mg concentration. By modeling the near-infrared-to-vacuum-ultraviolet ellipsometry data, information about layer thickness, electronic interband transitions, as well as surface roughness is extracted in dependence of the Mg concentration. A parameterized model that accounts for the phonon-plasmon coupling is applied for the infrared spectral range to determine the free-charge carrier concentration and mobility parameters in the doped bulk InN layer as well as the GaN template and undoped InN buffer layer. The optical Hall-effect best-match model parameters are consistent with those obtained from infrared ellipsometry analysis.

Effect of Al<sub>2</sub>O<sub>3</sub> Capping Layer in ZnO TFT Fabricated by Atomic Layer Deposition

In this paper, the electrical and physical analysis is carried out to investigate the effect of Al2O3 capping layer on ZnO film using atomic layer deposition. ZnO TFTs shows the metallic conduction behavior as Al2O3 capping layer thickness increases. From SIMS analysis, it is found out that the diffusion of Al into ZnO film is enhanced according to Al2O3 capping layer thickness. Moreover, the defects related to oxygen such as oxygen vacancy increase from XPS analysis and ZnO films reveal less compressive stress by substitution of Zn with Al form XRD analysis. That is, the metallic conduction behavior of ZnO TFTs with Al2O3 capping layer can be explained due to increase in the carrier concentration in ZnO channel layer from oxygen vacancy and substitution of Zn with Al.

Device characteristics of InSnO thin-film transistors with a modulated channel

The device performance of channel-modulated InSnO thin-film transistors (TFTs) was investigated. The field-effect mobility in the channel-modulated TFTs with a high carrier concentration layer at the channel/gate insulator interface was enhanced due to the increased carrier concentration. The insertion of the high carrier concentration layer at the channel/electrode interface improved the device performance due to reduction of the parasitic resistance. These results indicated that the device characteristic of TFTs can be enhanced by the modulated channel structure.

Temperature Dependence of Inversion Layer Carrier Concentration and Hall Mobility in 4H-SiC MOSFETs

Hall measurements on NO annealed 4H-SiC MOS gated Hall bars are reported in the temperature range 77 K- 423 K. The results indicate higher carrier concentration and lower trapping at increased temperatures, with a clear strong inversion regime at all temperatures. In stark contrast to Si, the Hall mobility increases with temperature for 77 K-373K, above which the mobility decreases slightly. The maximum experimental mobility was found to be ~50 cm2 V-1 s-1 which is only about 10% of the 4H-SiC bulk mobility indicating that while NO annealing drastically improves trapping, it does not improve the mobility significantly. Supporting modeling results strongly suggest the presence of a disordered SiC channel region.

Localization effect of a current-path in amorphous In–Ga–Zn–O thin film transistors with a highly doped buried-layer

The highly-doped buried layer (carrier concentration of ~ 10 19 cm − 3 ) in an amorphous indium–gallium–zinc oxide (a-IGZO) channel layer of thin film transistor (TFT) led to dramatic improvements in the performance and prolonged bias-stability without any high temperature treatment. These improvements are associated with the enhancement in density-of-states and carrier transport. The channel layer is composed of Ga-doped ZnO (GZO) and a-IGZO layers. Measurements performed on GZO-buried a-IGZO (GB-IGZO) TFTs indicate enhanced n-channel active layer characteristics, such as V th, μ FE, I off, I on/off ratio and S.S, which were enhanced to 1.2 V, 10.04 cm 2/V·s, ~ 10 −13A, ~ 10 7 and 0.93 V/decade, respectively. From the result of simulation, a current path was well defined through the surface of oxide active layer especially in GB-IGZO TFT case because the highly-doped buried layer plays the critical role of supplying sufficient negative charge density to compensate the amount of positive charge induced by the increasing gate voltage. The mechanism underlying the high performance and good stability is found to be the localization effect of a current path due to a highly-doped buried layer, which also effectively screens the oxide bulk and/or back interface trap-induced bias temperature instability.

Energy Band Control of GaAsSb-Based Backward Diodes to Improve Sensitivity of Millimeter-Wave Detection

The effect of energy band control with varying carrier concentration in GaAsSb-based backward diodes was investigated and diode parameters were analyzed to enhance voltage sensitivity. The backward diodes consisted of a heterojunction of p-GaAs0.51Sb0.49/i-In0.52Al0.48As/n-In0.63Ga0.37As/n-In0.53Ga0.47As, and they were mostly lattice-matched to an InP substrate. The degree of energy band bending at the depletion layer in n-In0.63Ga0.37As was varied on the basis of the carrier concentration in the n-In0.53Ga0.47As band control layer. Voltage sensitivity depends on carrier concentration since the concentration affects the band bending structure at the junction. The parameter analysis indicated that junction capacitance decreased when the carrier concentration in the band control layer decreased. When the carrier concentration in the band control layer was as low as 5×1018 cm-3, with the diode mesa at a diameter of 2.0 µm, an unmatched voltage sensitivity of 1495 V/W was obtained.

Inversion layer carrier concentration and mobility in 4H–SiC metal-oxide-semiconductor field-effect transistors

Free electron concentration and carrier mobility measurements on 4H–SiC metal-oxide-semiconductor inversion layers are reported in this article. The key finding is that in state-of-the-art nitrided gate oxides, loss of carriers by trapping no longer plays a significant role in the current degradation under heavy inversion conditions. Rather, it is the low carrier mobility (maximum∼60 cm2 V−1 s−1) that limits the channel current. The measured free carrier concentration is modeled using the charge-sheet model and the mobility is modeled by existing mobility models. Possible mobility mechanisms have been discussed based on the modeling results.

SiC epitaxial layers grown by chemical vapour deposition and the fabrication of Schottky barrier diodes

This paper presents the results of unintentionally doped 4H-SiC epilayers grown on n-type Si-faced 4H-SiC substrates with 8° off-axis toward the [112̄0] direction by low pressure horizontal hot-wall chemical vapour deposition. Growth temperature and pressure are 1580 °C and 104 Pa, respectively. Good surface morphology of the sample is observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) are used to characterize epitaxial layer thickness and the structural quality of the films respectively. The carrier concentration in the unintentional 4H-SiC homoepitaxial layer is about 6.4×1014 cm−3 obtained by C–V measurements. Schottky barrier diodes (SBDs) are fabricated on the epitaxial wafer in order to verify the quality of the wafer and to obtain information about the correlation between background impurity and electrical properties of the devices. Ni and Ti/4H-SiC Schottky barrier diodes with very good performances were obtained and their ideality factors are 1.10 and 1.05 respectively.

Effect of material parameters on the open-circuit voltage in a GaInAsSb thermophotovoltaic cell

In this paper, a numerical simulation on the open-circuit voltage ( V OC ) of the P-GaSb window/ P-Ga 0.8In 0.2As 0.18Sb 0.82 emitter/ N-Ga 0.8In 0.2As 0.18Sb 0.82 base/ N-GaSb structure thermophotovoltaic (TPV) cell is performed and an analysis of the effects of device parameters on V OC is presented. The simulations are carried out with the fixed spectral control filter and for the radiator temperature of T rad = 950 °C, cell temperature of T dio = 27 °C, the radiation photons are injected from the front P-region. The thick P-Ga 0.8In 0.2As 0.18Sb 0.82 emitter with the longer minority carrier diffusion length is the main optical absorption region. The simulated results are compared with the available experimental data, and a good agreement is obtained. The effects of the layer thickness, carrier concentration, injection level and main recombination mechanisms (e.g. the radiative, Auger, bulk Shockley–Read–Hall (SRH) and surface recombination) of the P-Ga 0.8In 0.2As 0.18Sb 0.82 emitter and N-Ga 0.8In 0.2As 0.18Sb 0.82 base on V OC are analyzed. It indicates that the parameters of the emitter region have stronger effect than that of the base region on V OC . Dependence of V OC on the material parameters of P-GaSb window layer is also analyzed, both the carrier concentration and thickness of P-GaSb window layer have effect on V OC . Moreover, adding a back surface reflector (BSR) to the TPV cell can increase V OC .

In‐situ doping and implantation of GaN layers with Mn

AbstractIn this paper we present a growth of Ga1–xMnxN layers by MOVPE and ion implantation of GaN layers with Mn. The Mn concentration detected by electron microprobe and PIXE was well below the solubility limit, ranging from 0.2 to 1.1 at.%. Implanted doses of Mn ions were in the range 1x1016‐5x1016 Mn atoms.cm–2 with energy of 330 keV. The analysis of the MOVPE deposition process of Ga1–xMnxN thin films revealed an unfavorable ratio between the apparent Mn concentration in the gas phase and its doping level in the deposited layer. On the other hand, the incorporation of Mn has a positive effect on the resulting surface morphology. The optimal deposition temperature of 1000 °C was found out as a compromise between the layer quality and Mn concentration. In both in‐situ grown and implanted samples, a ferromagnetic component persisting up to room temperature and a prevailing paramagnetic phase were observed. The ferromagnetic moment observed in implanted samples was influenced by free carrier concentration in GaN layers which were used for implantation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of thermal annealing to the characteristics of AlGaInP/GaInP multiple quantum wells light-emitting diode wafers

The influence of thermal annealing to the characteristics of AlGaInP/GaInP multiple quantum wells (MQWs) light-emitting diode wafers was studied by means of electrochemical capacitance–voltage (ECV) and photoluminescence (PL). Compared with the sample unannealed, the hole carrier concentration of p-GaP layer increased from 5.5×1018 to 6.5×1018cm−3, and the hole carrier concentration of p-AlGaInP layer increased from 6.0×1017 to 1.1×1018cm−3, after wafer was annealed at 460°C for 15min in nitrogen. The hole carrier concentrations of p-GaP layers and p-AlGaInP layers did not obviously change when the annealing temperature varied from 460 to 700°C. However, after the sample was annealed under 780°C for 15min, the hole carrier concentration of p-GaP layer and p-AlGaInP layer decreased to 8×1017 and 1.7×1017cm−3, respectively. At the same time, the diffusion of Mg atoms was observed.

Terahertz conductivity of localized photoinduced carriers in a Mott insulatorYTiO3 at low excitation density, contrasted with the metallic nature in a band semiconductorSi

We performed optical-pump terahertz-probe measurements of a Mott insulatorYTiO3 and a band semiconductor Si using a laser diode (1.47 eV) and a femtosecond-pulselaser (1.55 eV). Both samples possess long energy-relaxation times (1.5 ms forYTiO3 and 15 µs for Si); therefore, it is possible to extract terahertz complex conductivities of photoinducedcarriers under equilibrium. We observed highly contrasting behaviour—Drudeconductivity in Si and localized conductivity possibly obeying the Jonscher law inYTiO3. The carrier number at the highest carrier-concentration layer inYTiO3 is estimated to be 0.015 per Ti site. Anisotropic conductivity ofYTiO3 is determined. Our study indicates that localized carriers might play an important rolein the incipient formation of photoinduced metallic phases in Mott insulators.In addition, this study shows that the transfer-matrix method is effective forextracting an optical constant of a sample with a spatially inhomogeneous carrierdistribution.

Carrier concentration and surface electron accumulation in indium nitride layers grown by high pressure chemical vapor deposition

Electronic and structural properties of InN layer grown by high pressure chemical vapor deposition have been studied by high-resolution electron energy loss spectroscopy (HREELS) and room temperature infrared reflection measurements. HREEL spectra after atomic hydrogen cleaning exhibit N–H bending and stretching vibrations with no indications of an indium overlayer or droplet formation. Broad conduction band plasmon excitations are observed centered at 3100–4200cm−1 at various locations across the surface in HREEL spectra acquired with 25eV incident electron energy. The plasmon excitations are shifted about 300cm−1 higher in spectra acquired using 7eV electrons due to higher plasma frequency and carrier concentration at the surface than in the bulk which indicates surface electron accumulation. Infrared reflectance data acquired at various spots across the surface showed a similar variation in bulk plasma frequency. A three phase thin film reflection model fitted to the infrared data yielded carrier concentrations from 8.2×1019to1.5×1020cm−3 and carrier mobilities from 105 to 210cm2∕Vs.

Interaction between dislocations density and carrier concentration of gallium nitride layers

We investigated the problem of oxygen-dislocations interaction and its influence on carrier concentration in GaN layers. We achieved the samples with various dislocation density. Then we checked carrier concentration by means of Hall measurements. The samples with a higher EPD were characterized by a higher electron concentration. We assumed that oxygen diffuses along the threading dislocation lines, acts as a shallow donor and influences unintentional doping. Hence, the more dislocations present in GaN layers, the higher carrier concentration.

Determination of the carrier concentration in doped n-GaAs layers by Raman and light reflection spectroscopies

The carrier concentrations in Si-doped n-GaAs films have been determined by Raman and light reflection spectroscopies. The data obtained are in good agreement with the results of Hall measurements. It is shown that the light reflection and Raman spectroscopies supplement each other in determination of carrier concentrations in the range 1017−1019 cm−3.

Effect of Rapid Thermal Annealing on the Atomic Intermixing of Zn- and C-Doped InGaAs ∕ AlGaAs Quantum Well Laser Structures

We have studied the effect of annealing on the atomic intermixing of Zn- and C-doped laser structures. Electrochemical capacitance voltage measurements revealed that the carrier concentration in the Zn-doped contact layers decreased after annealing at for , indicating that some of the Zn acceptors were passivated or outdiffused from the surface, whereas in the C-doped samples there was an increase of the carrier concentration after annealing. This latter was confirmed by X-ray rocking curve results where there was an increase in the amount of lattice contraction associated with the presence of the substitutional carbon after annealing. Secondary ion mass spectroscopy revealed that the Zn diffused significantly from the top layers to the rest of the structures after annealing at , but the SIMS profile did not change significantly for C-doped samples with annealing. This indicates that Zn has a much higher mobility in comparison to carbon. Photoluminescence measurements after etching the samples to various depths showed similar luminescence defects in both Zn- and C-doped samples. The possible mechanism of atomic intermixing for both Zn- and C-doped samples are discussed.