Carrier Inversion Research Articles

Oxygen Vacancy-Tailored Schottky Heterojunction Activates Interface Dipole Amplification and Carrier Inversion for High-Performance Potassium-Ion Batteries.

An oxygen vacancy-tailored Schottky heterostructure composed of polyvinylpyrrolidone-assisted Bi2 Sn2 O7 (PVPBSO) nanocrystals and moderate work function graphene (mWFG, WF = 4.36eV) is designed, which in turn intensifies the built-in voltage and interface dipole across the space charge region (SCR), leading to the inversion of majority carriers for facilitating K+ transport/diffusion behaviors. Thorough band-alignment experiments and interface simulations reveal the dynamics between deficient BSO and mWFG, and how charge redistribution within the SCR leads to carrier inversion, demonstrating the impact of different defect engineering degrees on the amplification of Schottky junctions. The ordered transport of bipolar carriers can boost electrons and K ions easily passing through the inner and outer surfaces of the heterostructure. With high activity and low resistance in electrochemical reactions, the PVPBSO/mWFG exhibits an attractive capacity of 430mA h g-1 and a rate capability exceeding 2000mA g-1 , accompanied by minimal polarization and efficient utilization of conversion-alloying reactions. The substantial cell capacity and high-redox plateau of PVPBSO/mWFG//PB contribute to the practical feasibility of high-energy full batteries, offering long-cycle retention and high-voltage output. This study emphasizes the direct importance of interface and junction engineering in improving the efficiency of diverse electrochemical kinetic and diffusion processes for potassium-ion batteries.

Controlled p-Type Doping of Pyrite FeS2.

Pyrite FeS2 has extraordinary potential as a low-cost, nontoxic, sustainable photovoltaic but has underperformed dramatically in prior solar cells. The latter devices focus on heterojunction designs, which are now understood to suffer from problems associated with FeS2 surfaces. Simpler homojunction cells thus become appealing but have not been fabricated due to the historical inability to understand and control doping in pyrite. While recent advances have put S-vacancy and Co-based n-doping of FeS2 on a firm footing, unequivocal evidence for bulk p-doping remains elusive. Here, we demonstrate the first unambiguous and controlled p-type transport in FeS2 single crystals doped with phosphorus (P) during chemical vapor transport growth. P doping is found to be possible up to at least ∼100 ppm, inducing ∼1018 holes/cm3 at 300 K, while leaving the crystal structure and quality unchanged. As the P doping is increased in crystals natively n-doped with S vacancies, the majority carrier type inverts from n to p near ∼25 and ∼55 ppm P, as detected by Seebeck and Hall effects, respectively. Detailed temperature- and P-doping-dependent transport measurements establish that the P acceptor level is 175 ± 10 meV above the valence band maximum, explain details of the carrier inversion, elucidate the relative mobility of electrons and holes, reveal mid-gap defect levels, and unambiguously establish that the inversion to p-type occurs in the bulk and is not an artifact of hopping conduction. Such controlled bulk p-doping opens the door to pyrite p-n homojunctions, unveiling new opportunities for solar cells based on this extraordinary semiconductor.

The Limit Tuning Effects Exerted by the Mechanically Induced Artificial Potential Barriers on the I-V Characteristics of Piezoelectric PN Junctions.

A mechanically induced artificial potential barrier (MIAPB) in piezoelectric semiconductor devices is set up under the action of a pair of tensile/compressive mechanical loadings. Three factors, namely, the barrier height, width and position, affect the nature and extent of interaction between the MIAPB and the contact barrier, and the tuning characteristics (generated under conditions of the artificial barrier) of the piezoelectric PN junctions were studied. The influence of these factors resulted in variations in the interaction intensities, superposition effects, carrier inversion degrees and carrier redistribution ranges. Subsequently, the limit tuning effects exerted by the tensile/compressive-mode MIAPB on the PN junctions were studied. The inconsistency between the left and right end of the tensile-mode MIAPB under conditions of the offset loading state proves that the maximum tuning effect is generated when both sides of the interface are symmetrically loaded. The range of carrier redistribution and the over-inversion of local carriers, affected by the width and height of MIAPB, result in a second competitive mechanism. The carrier redistribution range and the carrier inversion degree require that the compressive-mode MIAPB be sufficiently wide. The interaction intensities and the superposition effects, affected by the position and height of the MIAPB, contribute to the second competing mechanism. We logically clarify the relationship between multiple competition and find that the emergence of multiple competitive mechanisms proves the existence of the limit tuning effect of MIAPB on the I-V properties of PN junctions. The results reported herein provide a platform for understanding the mechanical tuning laws governing the functions of piezoelectric PN junctions and piezoelectric devices.

A rigorous Fermi-Dirac statistics-based MOSFET channel surface potential equation using polylogarithms

The MOSFET channel Surface Potential Equation (SPE), being the fundamental building block of all Surface Potential (SP)-based MOSFET compact models, must be as physically faithful as possible. To that end, in this article we propose a novel alternative form of the SPE, which is valid under many circumstances and operating conditions (e.g. degenerate doping, incomplete dopant ionization, strong carrier inversion and accumulation, cryogenic operation) where the occupation probabilities of charges cannot be well described by the Maxwell-Boltzmann (MB) statistics approximation. Thus, to more accurately describe free charge carrier densities they are defined here by their corresponding Fermi-Dirac Integrals (FDI). But, unlike previous formulations of the SPE directly expressed in terms of FDIs or some analytic approximation thereof, in our formulation we substitute from the beginning the FDIs by their equivalent polylogarithm representations, before integrating Poisson’s equation to obtain the proposed SPE. Since polylogarithms are functions that may be analytically differentiated and integrated, and because there already exist well established algorithms and software routines for their efficient numerical computation, the proposed polylogarithmic form of the MOSFET channel SPE constitutes a more accurate alternative to existing SPE approximate forms.

Charge Carrier Inversion in a Doped Thin Film Organic Semiconductor Island.

Inducing an inversion layer in organic semiconductors is a highly nontrivial, but critical, achievement for producing organic field-effect transistor (OFET) devices, which rely on the generation of inversion, accumulation, and depletion regimes for successful operation. Here, we develop a pulsed bias technique to characterize the dopant type of any organic material system, without prior knowledge or characterization of the material in question. We use this technique on a pentacene/PTCDI heterostructure and thus deduce that pentacene is exhibiting n-doped like response. The source of the additional charges in the pentacene island can be identified by charging rings in the dissipation channel of the noncontact atomic force microscopy (AFM) signal, a typical signature for localized charge transfer from the AFM tip to the sample. Additionally, through tip-induced band-bending, we generate inversion, depletion, and accumulation regimes over a 20 nm radius, three monolayer thick n-doped pentacene island. Our findings demonstrate that nanometer-scale lateral extent and thickness are sufficient for an OFET device to operate in the inversion regime.

Degradation study of carrier selective contact silicon solar cells with ageing: Role of silicon surface morphology

Ageing effect on the performance of Ag/ITO/MoOx/n-Si/LiFx/Al carrier selective contact (CSC) silicon solar cells has been investigated based on silicon surface morphology (planar, different pyramid sizes, and chemical polishing of pyramids). The cells with small silicon pyramids (~2 µm) have shown better stability with time than the medium/large pyramids (~5/~8 µm). The chemical polishing of pyramid peaks and valleys has further reduced the cells ageing effect due to minimization of the microstructural stress (tensile in the valleys and compressive at the peaks) at the MoOx/n-Si interface, which has been verified indirectly with cells fabricated on a planar surface. The cell’s performance degradation based on morphology points out the instability of the MoOx layer and Schottky barrier reduction, which results in hole-transport hindrance at the MoOx/n-Si junction with the S-shape in J-V graphs under illumination. The ageing effect on device performance is further investigated using the Sentaurus TCAD simulations with the MoOx layer work function variation, and the study indicates the band bending reduction (minimal carrier inversion) and hole transport barrier at the junction region.

Investigation of silicon surface passivation by sputtered amorphous silicon and thermally evaporated molybdenum oxide films using temperature- and injection-dependent lifetime spectroscopy

Crystalline silicon (c-Si) surface passivation has been investigated by sputtered hydrogenated intrinsic amorphous silicon (S-i-a-Si:H) and thermally evaporated molybdenum oxide (MoOx) thin films. The temperature- and injection-dependent lifetime spectroscopy technique has been adopted for analyzing the passivation quality of the c-Si surface, using parameters such as the minority carrier effective lifetime (τeff), the activation energy of surface/interface defect states (ΔE), and the electron to hole carrier capture cross-section ratio (k) at the interface. With S-i-a-Si:H films, a τeff of ∼70 µs and ΔE of ∼51 meV have been observed in comparison to a τeff of ∼110 µs and ΔE of ∼109 meV from the MoOx films. These entirely different parameters are an indication of the relatively strong carrier recombination with dense interface/surface states from the S-i-a-Si:H passivation layers. The S-i-a-Si:H layers are unable to minimize the c-Si surface trap states with the chemical passivation for reducing carrier recombination due to the generation of additional surface defect states by the sputtering damage. However, the MoOx layers show better c-Si surface passivation due to the reduction of majority carriers by the carrier inversion (field-effect passivation) and chemical passivation. This effect is clearly reflected with the opposite trend in the carrier capture analysis from S-i-a-Si:H and MoOx layers.

Photodiode characteristics of HfO2 thin films prepared by magnetron sputtering

HfO2 thin film is deposited on p-Si substrates by RF magnetron sputtering apparatus and annealed at 750 °C for 10 min with O2 atmosphere. Spectral analysis shows that HfO2 thin films have good transmittance to light, especially ultraviolet band. The HfO2 layers belong monoclinic phase and its thickness is about 50 nm. In the Au/HfO2/p-Si structure, photodiode characteristics were studied at room temperature and compared with the light current generated under white light, the response current generated under ultraviolet light is more prominent. The photocurrent reaches 80 μA and the repeatable response of device under 23.5 mW/cm2 ultraviolet illuminating is stable. It's found that the working mechanism of this photodiode could have three different states: the majority carrier stacking state of reverse bias, the majority carrier depletion state of forward bias with dark condition and the minority carrier inversion state of forward bias with ultraviolet illumination. The device also has a high damage threshold and its photocurrent is still not saturated at bias 8 V, indicating that it can be applied as a new type of UV detector.

Delay-Based Reservoir Computing Using Multimode Semiconductor Lasers: Exploiting the Rich Carrier Dynamics

Delay-based reservoir computing is a neuromorphiccomputing technique employing a single nonlinear node, in this case a semiconductor laser subjected to a delayed optical self-feedback. This implementation of reservoir computing, while being versatile and highly performant, is limited in processing speed by the delay length. In an effort to reduce the required delay line length, while maintaining the same strong performance, we investigate if it is possible to distribute the processing power over more than one longitudinal mode. We therefore have numerically analysed a rate equation model of a semiconductor laser with two longitudinal modes, delayed optical feedback and optical injection. Our modelling takes into account the carrier inversion moments that represent carrier gratings formed in the cavity during operation. This allows us to study the importance of modal interaction via carrier gratings and how this effects the computational power. We show that the setup with a dual-mode laser and an optimized reservoir parameter space, can reduce the delay-line fourfold in comparison with a single-mode laser setup.

Electrical transport properties of sensitized PbSe thin films for IR imaging sensors

Electrical transport properties of sensitized PbSe thin films for IR imaging applications were investigated. PbSe thin films were deposited by Chemical Bath Deposition (CBD) method. To sensitize the film, oxidation at 460 °C and iodization at 350 °C were performed successively. As-grown PbSe thin films showed p-type conduction due to Se-rich condition with carrier concentrations, mobility of and electrical resistivity of PbSe thin film after oxidation, the carrier density, mobility and resistivity values were and However, the carrier type was still p-type after oxidation. After sensitization (oxidation and iodization), PbSe thin film showed p-type behavior with carrier concentration of mobility of and resistivity of Iodine-rich PbI2 phase is formed on the top part of the film after iodization. Therefore, this I-rich PbI2 phase still generates p-type conduction without any carrier inversion. A PbI2/PbSe thin film structure showed pp isotype heterojunction characteristics after sensitization. No photoluminescence (PL) signal was observed from as grown thin films and oxidized PbSe thin film showed a peak at 285 meV. After sensitization, a significantly intense IR fluorescence peak from the band gap at 291 meV was observed. The peak height from sensitized PbSe thin film is 12 times higher than that of oxidized PbSe possibly the recombination of photo-generated electron-hole pairs was effectively suppressed. In addition, dark current as a function of temperature in as-grown, oxidized and sensitized PbSe was investigated and results showed the grain boundary activation energy values of 31 meV, 57 meV and 96 meV respectively, which may act as a sensitizing center for electron trapping. In summary, electrical properties data for as grown, oxidized and sensitized PbSe thin films are presented and temperature dependence studies indicates electron trapping mechanism for photoconductivity.

Non-equilibrium dynamics in the dual-wavelength operation of vertical external-cavity surface-emitting lasers.

Microscopic many-body theory coupled with Maxwell's equation is used to study dual-wavelength operation in vertical external-cavity surface-emitting lasers. The intrinsically dynamic nature of coexisting emission wavelengths in semiconductor lasers is associated with characteristic non-equilibrium carrier dynamics, which causes significant deformations of the quasi-equilibrium gain and carrier inversion. Extended numerical simulations are employed to efficiently investigate the parameter space to identify the regime for dual-wavelength operation. Using a frequency selective intracavity etalon, two families of modes are stabilized with dynamical interchange of the strongest emission peaks. For this operation mode, anti-correlated intensity noise is observed in agreement with the experiment. A method using effective frequency selective filtering is suggested for stabilization of genuine dual-wavelength output.

LAMBERT FUNCTION METHODs TO STUDY LASER DYNAMICS WITH TIME-DELAYED FEEDBACK

<p><!--StartFragment-->Time-delayed differential equations arise frequently in the study of nonlinear dynamics of lasers with optical feedback and because the analytical solution of such equations can be intractable, one resorts to numerical methods. In this manuscript, we show that under some conditions, the rate equations model that is used to model semiconductor lasers with feedback can be analytically solved by using the Lambert W function. In particular, we discuss the conditions under which the coupled rate equations for the intracavity electric field and carrier inversion can be reduced to a single equation for the field, and how this single rate equation can be cast in a form that is amenable to the use of the Lambert W function.<!--EndFragment--></p>

(Keynote) Lasing from SiGeSn/GeSn Multiple Quantum Well Structures

The amount of data collected, transferred and processed increased over the last decade with a substantial annual rate. With the internet of things in sight, this trend will be continued. Already today more than 10% of the electrical power produced in the western world is consumed by IT products, underlining the demand to drastically reduce the power consumption. In fact, energy consumption will be the main driver of development in information technology. Silicon photonics is considered to be an attractive pathway to drastically reduce power consumption in information technology based on classical Si microelectronics /1/. Moreover Si photonics are envisioned also as a promising pathway towards quantum computing/2/. Group IV alloys, namely Ge and SiGe on Si, are heavily investigated for the integration of modulators and detectors on Si. However, higher integration levels of optical data transfer on the chip will require the integration of low power laser. The latter is approached by a wide range of technologies to deposit III/V structures on Si as well as by bonding III/V lasers Si. Recently, a direct bandgap as well as optically pumped lasing was demonstrated for GeSn alloys deposited on Ge virtual substrates on Si (100) 8” wafers. Here, efforts are reported of this ongoing endeavor towards an electrically pumped group IV laser. The group IV alloy GeSn provide a direct band gap for Sn concentration above ~8%, which is far beyond the solid solubility limit of ~1%. Recently high quality GeSn alloys with Sn concentrations up to 14.5% could be grown at low temperatures and high growth rates by means reactive gas source epitaxy. These GeSn have a direct band gap, in the range of 0.48-0.63 eV dependening on the Sn concentration. Phosphorous and Boron doping has been realized to fabricate p-i-n junction in SiGeSn/GeSn structures. Thus these materials pave the road for the integration of optoelectronic circuitry on Si (100) substrates. Optically pumped laser in the Fabry Perot geometry as well as microdisc lasers have been fabricated from GeSn films, SiGeSn double heterostructures and SiGeSn/GeSn multiple quantum wells (MQW) on Ge virtual substrates. The threshold required to achieve lasing dropped from ~300 kW/cm2 for a thick GeSn film to about 30 kW/cm2 for a MQW structure. This can be attributed to reduced optical losses due to surface scattering as well as due to the reduced number of states in the multiple quantum wells, which allows carrier inversion at smaller pumping powers. However, due to the very small effective mass of electrons in the Г valley compared to large mass in the L valley, the quantum wells have to be designed carefully. For thin quantum wells the confinement shift of the subbands of the Г valley is larger than that for the L valley reducing the directness and may even turn it into an indirect material. Moreover, a (Si)GeSn buffer layer above critical thickness is required to relax the strain before the growth of the active region of the laser. The strain relaxation occurs predominantly via 90° step edge dislocations at the Ge/GeSn interface, within the hetero- and MQW structures no dislocations were detected by cross sectional TEM. However, besides defect engineering, care has to be taken in the design of the structures also to avoid losses due to absorption in GeSn and SiGeSn cladding layers, since the limited band offsets give rather stringent design rules. To achieve electrically pumped lasing double hetero- and MQW-structures have been grown using SiGeSn cladding and barrier layers. Parts of the SiGeSn cladding layers have been doped by P and B to achieve p-i-n junctions. First devices have been fabricated showing a superior electroluminescence efficiency of MQW structures compared to hetero- of homojunction devices. /1/ R. Soref, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 12, 1678 (2006) /2/ T. Rudolph APL PHOTONICS 2, 030901 (2017)

Reticulated shallow etch mesa isolation for controlling surface leakage in GaSb-based infrared detectors

Longwave infrared detectors using p-type absorbers composed of InAs-rich type-II superlattices (T2SLs) nearly always suffer from high surface currents due to carrier inversion on the etched sidewalls. Here, we demonstrate reticulated shallow etch mesa isolation (RSEMI): a structural method of reducing surface currents in longwave single-band and midwave/longwave dual-band detectors with p-type T2SL absorbers. By introducing a lateral shoulder to increase the separation between the n+ cathode and the inverted absorber surface, a substantial barrier to surface electron flow is formed. We demonstrate experimentally that the RSEMI process results in lower surface current, lower net dark current, much weaker dependence of the current on bias, and higher uniformity compared to mesas processed with a single deep etch. For the structure used, a shoulder width of 2 μm is sufficient to block surface currents.

Correlation of Bandgap Reduction with Inversion Response in (Si)GeSn/High-k/Metal Stacks.

The bandgap tunability of (Si)GeSn group IV semiconductors opens a new era in Si-technology. Depending on the Si/Sn contents, direct and indirect bandgaps in the range of 0.4-0.8 eV can be obtained, offering a broad spectrum of both photonic and low power electronic applications. In this work, we systematically studied capacitance-voltage characteristics of high-k/metal gate stacks formed on GeSn and SiGeSn alloys with Sn-contents ranging from 0 to 14 at. % and Si-contents from 0 to 10 at. % particularly focusing on the minority carrier inversion response. A clear correlation between the Sn-induced shrinkage of the bandgap energy and enhanced minority carrier response was confirmed using temperature and frequency dependent capacitance voltage-measurements, in good agreement with k.p theory predictions and photoluminescence measurements of the analyzed epilayers as reported earlier. The enhanced minority generation rate for higher Sn-contents can be firmly linked to the bandgap reduction in the GeSn epilayer without significant influence of substrate/interface effects. It thus offers a unique possibility to analyze intrinsic defects in (Si)GeSn epilayers. The extracted dominant defect level for minority carrier inversion lies approximately 0.4 eV above the valence band edge in the studied Sn-content range (0-12.5 at. %). This finding is of critical importance since it shows that the presence of Sn by itself does not impair the minority carrier lifetime. Therefore, the continuous improvement of (Si)GeSn material quality should yield longer nonradiative recombination times which are required for the fabrication of efficient light detectors and to obtain room temperature lasing action.

Heteroclinic dynamics of coupled semiconductor lasers with optoelectronic feedback.

Generalized Lotka-Volterra (GLV) equations are important equations used in various areas of science to describe competitive dynamics among a population of N interacting nodes in a network topology. In this Letter, we introduce a photonic network consisting of three optoelectronically cross-coupled semiconductor lasers to realize a GLV model. In such a network, the interaction of intensity and carrier inversion rates, as well as phases of laser oscillator nodes, result in various dynamics. We study the influence of asymmetric coupling strength and frequency detuning between semiconductor lasers and show that inhibitory asymmetric coupling is required to achieve consecutive amplitude oscillations of the laser nodes. These studies were motivated primarily by the dynamical models used to model brain cognitive activities and their correspondence with dynamics obtained among coupled laser oscillators.

Towards p-Type Conductivity in SnO2 Nanocrystals through Li Doping and Its Applications in Porous Diodes for Room Temperature Chlorine Gas Detection

This work examined electrical transport properties and Li doping in SnO2 synthesized by the sol–gel method. Solid-state 7Li-NMR line shapes revealed that Li ions occupy two distinct sites with differing dynamic mobilities. The chemical exchange rate between the two sites is, however, too slow for detection on the NMR timescale. Compressed nanoparticulate films of this doped semiconductor exhibited a positive Seebeck coefficient implying a p-type conductivity. A variable-temperature direct current conductivity, over a 25–350 °C temperature range, followed an Efros–Shklovskii variable range hopping (ES-VRH) conduction mechanism (ln(ρ) versus T −1/2) at temperatures below 100 °C with a crossover to 2D Mott variable range hopping (M-VRH) (ln(ρ) versus T −1/3) conduction at temperatures above 250 °C. In a transition region between these two limiting behaviors, direct current resistivity exhibited an anomalous temperature-independent plateau. We suggest that its origin may lie in a carrier inversion phenomenon wherein the majority carriers switch from holes to electrons due to Li ion expulsion from the crystalline core and creation of oxygen vacancies generated by loss of oxygen at elevated temperatures. Using a compression technique, porous diodes consisting of n-type (antimony doped SnO2) and the p-type (lithium-doped) nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference; owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. This access is not possible in conventional diodes fabricated through contemporary planar technology. The gas sensing properties of the diodes were investigated by using Cl2, Br2, HCl, NO, NO2, CHCl3, NH3 and H2. Of all the gases tested, the sensor had very good sensitivity to Cl2 and had a response of 80 at 400 ppb of Cl2. The response time of the sensor was ~30 s at room temperature but the recovery time was temperature dependent. At room temperature the recovery time was 80s after 400 ppb chlorine exposure. The sensors were also found to recover quickly (~ 30 s) when the junctions were biased. Reverse biasing the diode provides a controllable band-bending at a p-n junction that could influence the electron-transfer rates from the adsorbates which create intra-band localized states. As a result reverse biasing can provide a means of desorbing the analyzed species. This approach eliminates the requirement to remove adsorbates by elevating the sensor temperature and hence improves on the energy efficiency of these types of sensors.

Nonequilibrium plasmon emission drives ultrafast carrier relaxation dynamics in photoexcited graphene

The fast decay of carrier inversion in photoexcited graphene has been attributed to optical phonon emission and Auger recombination. Plasmon emission provides another pathway that, as we show here, drives the carrier relaxation dynamics on ultrafast timescales. In studying the nonequilibrium relaxation dynamics we find that plasmon emission effectively converts inversion into hot carriers, whose energy is then extracted by optical phonon emission. This mechanism not only explains the observed fs-lifetime of inversion but also offers the prospect for atomically thin ultrafast plasmon emitters.

Properties of p- and n-Type PbTe Microwires for Thermoelectric Devices

In thermopower measurements, microwires fabricated from as-purchased bulk PbTe exhibits p-type behavior between room temperature and ∼600 K. At higher temperatures, it undergoes majority carrier inversion and exhibits n-type behavior. We report on the preparation and properties of potassium oxide and Zn-doped PbTe microwires, which exhibit stable p- and n-type behavior, respectively, between room temperature and 725 K. Thermoelectric figures of merit (ZT) are reported for device components prepared from bundles of such p- and n-type microwires in a glass matrix.

Capacitance study of carrier inversion at the amorphous/crystalline silicon heterojunction passivated by different thicknesses of i-layer

• We studied silicon heterojunction samples with varied passivation i-layer thickness. • Measured activation energy from DLTS determines inversion at the heterojunction. • Coplanar conductance reflects interface inversion and confirms results from DLTS. • Inversion at the heterojunction is reduced with a growing thickness of the i-layer. The paper deals with the diagnostics of structures containing a heterojunction of amorphous and crystalline silicon representing the key part of the silicon heterojunction solar cell. The change of carrier inversion at the heterointerface by means of an intrinsic amorphous intermediate layer inserted at the heterointerface was confirmed by capacitance deep level transient spectroscopy and coplanar conductance measurements. A growing thickness of the intrinsic amorphous silicon layer brings about a decrease in the thickness of the inversion layer at the heterointerface, leading to higher recombination. The results emphasize the requirement for optimization of the interface with the regard to the trade-off between the thickness of the passivation layer and interface quality.