Capacitance-voltage Measurements Research Articles

Interfacial Metal Chlorides as a Tool to Enhance Charge Carrier Dynamics, Electroluminescence, and Overall Efficiency of Organic Optoelectronic Devices.

Interface engineering is the key to optimizing optoelectronic device performance, addressing challenges like reducing potential barriers, passivating interface traps, and controlling recombination of charges. Metal fluorides such as lithium fluoride are employed in interface modification within organic devices due to their strong dipole characteristics but carry health risks, high processing costs, and minimal impact on interface traps in organic electronics. Hence, this study investigates alternative metal chloride (MC) nanocrystals (sodium, cesium, rubidium, and potassium chlorides) that exhibit a strong dipole moment and are readily processable with the aim of reducing the influence of interface traps. Interfacial properties are assessed via various techniques, including electron paramagnetic resonance, X-ray/ultraviolet photoelectron spectroscopy, capacitance-voltage measurements, and density functional theory calculations. In organic light-emitting diodes (OLEDs), the influence of MC on charge transfer, trap density, and light emission properties is evaluated. MCs in ZnO:PEIE nanocomposites (NCs) show improved charge transport, accelerated trapping/detrapping in ZnO:PEIE NCs, and a 50% reduction in active traps in NaCl-based devices versus the reference without MCs. RbCl-, CsCl-, and NaCl-based OLEDs exhibit substantial reductions in the potential barrier between the electron injection layer and the metal contact (Al) from 4.43 to 2.93, 3.02, and 4 eV, respectively, accompanied by enhancements of 35, 27, and 25% in electroluminescence intensity.

Photo-capacitance measurement in dual-frequency mode and its application to study of Pt/κ-Ga2O3 planar Schottky diode

In this study, a dual-frequency method for the impedance/admittance measurements on illuminated junctions has been critically analyzed as an appropriate methodological approach for the measure of the depletion capacitance, both under steady-state light and during on-off illumination cycles. A planar Pt/κ-Ga2O3 Schottky diode was used as a test structure. Then capacitance-voltage (C-V) measurements were carried out under various applied AC frequencies and monochromatic UV-C light (λ = 254 nm) and compared to dark values. Transient photo-capacitance (TPC) measurements were performed at fixed applied voltages and the same AC frequencies and illumination conditions as the C-V measurements.Thanks to capacitance-frequency (C-f) measurements, the device under test was preliminary demonstrated to be well represented, both in dark and under light, by the equivalent circuit required for the applicability of the dual-frequency approach. It must include a depletion capacitance, parallel leakage resistance, and a series resistance. Dual-frequency capacitance resulted comparable to the single frequency C-V and TPC data obtained in the high-frequency limit for series configuration measurements and those obtained at low frequency in measurements carried out in parallel configuration.The experimental conditions of reliable data acquisition were discussed leading to the interpretation of the results in terms of the presence of slow-response traps.

A hBN/Ga2O3 pn junction diode.

The development of next-generation materials such as hBN and Ga2O3 remains a topic of intense focus owing to their suitability for efficient deep ultraviolet (DUV) emission and power electronic applications. In this study, we combine p-type hBN and n-type Ga2O3, forming a pseudo-vertical pn hBN/Ga2O3 heterojunction device. Rectification ratios > 105 (300K) and [Formula: see text]400 (475K) are observed and are amongst the highest values reported to date for ultra-thin hBN-based pn junctions. The measured current under forward bias is ~2mA, which we attribute to the shallow Mg acceptor level (60 meV), and 0.2 µA at -10V. Critically, device performance remains stable and highly repeatable after a multitude of temperature ramps to 475K. Capacitance-voltage measurements indicate widening the depletion region under increasing reverse bias voltage and a built-in voltage of 2.34V is recorded. The hBN p-type characteristic is confirmed by Hall effect, a hole concentration of [Formula: see text] cm-3 and mobility of 24.8 cm2/Vs is achieved. Mg doped hBN resistance reduces by >108 compared to intrinsic material. Future work shall focus on the optical emission properties of this material system.

Mercury-probe measurement of electron mobility in β-Ga2O3 using junction moderated dielectric relaxation

We demonstrate the junction-moderated dielectric relaxation method to measure the in-plane electron mobility in β-Ga2O3 epitaxial layers. Unlike the Hall technique and channel mobility measurement in field-effect transistors, this method does not require the deposition of permanent metal contacts. Rather, it measures the bias voltage and frequency dependence of the equivalent capacitance of the Mercury/β-Ga2O3/Mercury structure consisting of a Schottky contact, a quasi-neutral thin film semiconductor, and an Ohmic contact connected in series. The intrinsic dielectric relaxation of the bulk β-Ga2O3 semiconductor typically occurs at ∼1012 s−1, but when moderated by the Mercury/β-Ga2O3 Schottky junction, it manifests itself as an inflection in the capacitance-frequency characteristics at a much lower frequency of ∼106 s−1 within the range of most capacitance measuring instruments. Using carrier density and layer thickness determined from capacitance-voltage measurement, we extract the electron mobility of β-Ga2O3 from the junction-moderated dielectric relaxation frequency.

Separation of planar and edge contributions to total capacitance for accurate doping concentration determination in square silicon photodiodes

Accurately determining the doping concentrations of silicon photodiodes (PDs) is crucial for optimizing their performance in various applications. This study presents a methodology for separating the planar and edge contributions to the total capacitance of square silicon PDs with guard rings. Through capacitance-voltage measurements, we distinguished planar capacitance, which reflects the bulk properties of the silicon PD, from edge capacitance, influenced by device geometry and fringing fields. We demonstrated that the fabricated PDs with guard rings surrounding the active area could be effectively modeled using a coxial-like structure to estimate edge capacitance. Doping concentrations, depletion widths, and resistivities were determined through linear fitting of the inverse square of the measured capacitance per unit area as a function of the reverse bias voltage. All parameters obtained from the full depletion voltage Vd , determined by the intersection of the linear fits for V < Vd and V > Vd , demonstrated agreement within 1σ. Our results underscore the importance of accounting for edge effects to accurately determine doping concentrations from 1/C 2 vs. V plots.

Phonon-assisted leakage current of InGaN light emitting diode

We report on the leakage current mechanism in a blue GaN-based light-emitting diode (LED). The device structure was grown by the MOCVD technique on a sapphire substrate. The LED was characterized through various measurements including current-voltage, electroluminescence, and secondary ion mass spectroscopy (SIMS). Capacitance-voltage measurements were employed to calculate the depletion layer thickness at different bias voltages and to analyze the doping profile in the active layer. The reverse temperature-dependent current-voltage measurements were carried out to study the leakage mechanism. The leakage current was explained by phonon-assisted tunneling of charge carriers through deep trap states. The trap energy and density of states were extracted from the application of the introduced model. Cathodoluminescence measurements were performed to evaluate the density of dislocations, which were then compared to x-ray diffraction measurements. The determined value was close to the density of states obtained from the tunneling model.

Reduction of interface defects in gate-recessed GaN HEMTs by neutral beam etching

This study investigates and compares the impact of different etching techniques on the fabrication of GaN high electron mobility transistors (HEMTs) between the inductively coupled plasma reactive ion etching (ICP-RIE) and the neutral beam etching (NBE) for the gate recess. By conducting direct current analysis, it was found that devices manufactured using the NBE exhibited superior electrical performance as compared with those produced using the ICP-RIE. These enhanced electrical characteristics include a transconductance of up to 100.4 mS/mm, a threshold voltage (Vth) of −2.3 V, an on/off current ratio of 1.1 × 109, a subthreshold swing (S.S.) of 99.63 mV/dec, and a remarkably low gate leakage current. Additionally, we noted varying degrees of hysteresis in the I–V characteristics were related to process disparities possibly leading to interface defects. Multi-frequency capacitance-voltage (C–V) measurements were used to identify the interface defects at the oxide/AlGaN interface of the gate. The results revealed that devices fabricated using the NBE exhibited a lower interface defect density as compared with those fabricated using the ICP-RIE, thereby elucidating the reduced hysteresis observed in the I–V characteristics. These findings indicated the significant advantages of the NBE process in the fabrication of GaN HEMTs.

Microstructure Evolution and Electrical Behaviors for High-Performance Cu2O/Zr-Doped β-Ga2O3 Heterojunction Diodes.

Beta-gallium oxide (β-Ga2O3) is emerging as a promising ultrawide band gap (UWBG) semiconductor, which is vital for high-power, high-frequency electronics and deep-UV optoelectronics. It is especially significant for flexible wearable electronics, enabling the fabrication of high-performance Ga2O3-based devices at low temperatures. However, the limited crystallinity and pronounced structural defects arising from the low-temperature deposition of Ga2O3 films significantly restrict the heterojunction interface quality and the relevant electrical performance of Ga2O3-based devices. In this work, cuprous oxide (Cu2O)/Zr-doped β-Ga2O3 heterojunction diodes are fabricated by magnetron sputtering without intentional substrate heating, followed by an investigation into their microstructure and electrical behaviors. Zr doping can markedly enhance the Ga2O3 crystallinity at low substrate temperatures, transforming the amorphous structure of pristine Ga2O3 films into the crystallized β phase. Moreover, crystalline β-Ga2O3 facilitates the epitaxial growth of the Cu2O phase, suppressing the formation of detrimental secondary phase CuO at the heterojunction interface. Benefiting from the high-quality heterojunction interface, the Cu2O/Zr-doped β-Ga2O3 heterojunction diode exhibits a near-ideal electrical behavior with a low ideality factor of 1.6. The consistent electrical parameters extracted from current-voltage (J-V) and capacitance-voltage (C-V) measurements also confirm the high quality of β-Ga2O3. This work highlights the potential for the low-temperature production of high-quality β-Ga2O3-based heterojunction devices through Zr doping.

Interface Characterization of Graphene‐Silicon Heterojunction Using Hg Probe Capacitance–Voltage Measurement

AbstractInvestigating the intrinsic properties of the Schottky interface between graphene and 3D bulk silicon is crucial. However, the semiconductor technology introduces extra doping and defects in graphene, which significantly disturbs the property of the graphene‐silicon interface. Here, the interface parameters of graphene/n‐Si heterojunction are derived by the damage‐free Hg‐probe capacitance–voltage measurement. Due to its low‐density states, the Fermi level of graphene can be pushed upward, which results in a lower Schottky barrier height (ΦB0) of Hg/graphene/n‐Si (HGS) heterostructure than that of Hg/n‐Si (HS) structure. Additionally, the series resistance (Rs) of HGS becomes lower than that of HS, which can be attributed to the narrowed depletion layer width (WD) and the decreased interface state density (Nit). Furthermore, the frequency characteristic is also investigated. Because of the weak interface state charge trapping–detrapping process and the decreased Nit at high frequency, electrons will accumulate in graphene, and the Fermi level will be pushed up. Hence, the ΦB0 and Rs will decrease with increasing frequency. This study contributes to a deep understanding of the graphene/silicon heterojunction interfaces, which is crucial for designing and optimizing the new electronic and optoelectronic devices based on 2D/3D heterostructure.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

Comparative Study of Plasma-Enhanced-Atomic-Layer-Deposited Al2O3/HfO2/SiO2 and HfO2/Al2O3/SiO2 Trilayers for Ultraviolet Laser Applications.

High-performance thin films combining large optical bandgap Al2O3 and high refractive index HfO2 are excellent components for constructing the next generation of laser systems with enhanced output power. However, the growth of low-defect plasma-enhanced-atomic-layer-deposited (PEALD) Al2O3 for high-power laser applications and its combination with HfO2 and SiO2 materials commonly used in high-power laser thin films still face challenges, such as how to minimize defects, especially interface defects. In this work, substrate-layer interface defects in Al2O3 single-layer thin films, layer-layer interface defects in Al2O3-based bilayer and trilayer thin films, and their effects on the laser-induced damage threshold (LIDT) were investigated via capacitance-voltage (C-V) measurements. The experimental results show that by optimizing the deposition parameters, specifically the deposition temperature, precursor exposure time, and plasma oxygen exposure time, Al2O3 thin films with low defect density and high LIDT can be obtained. Two trilayer anti-reflection (AR) thin film structures, Al2O3/HfO2/SiO2 and HfO2/Al2O3/SiO2, were then prepared and compared. The trilayer AR thin film with Al2O3/HfO2/SiO2 structure exhibits a lower interface defect density, better interface bonding performance, and an increase in LIDT by approximately 2.8 times. We believe these results provide guidance for the control of interface defects and the design of thin film structures and will benefit many thin film optics for laser applications.

The electrical and dielectric features of Al/YbFeO3/p-Si/Al and Al/YbFe0.90Co0.10O3/p-Si/Al structures with interfacial perovskite-oxide layer depending on bias voltage and frequency

In this investigation, thin films of YbFeO3, both in its pure form and doped with 10% Co, were fabricated on a p-Si substrate at 500 °C through the radio-frequency magnetron sputtering method. Examination via Scanning Electron Microscopy demonstrated a porous texture for the pure sample, contrasting with a smooth and crack-free surface post-Co doping. Analysis via X-ray photoelectron spectroscopy unveiled Yb’s 3 + oxidation state, alongside the presence of lattice oxygen, oxygen vacancies, and adsorbed oxygen evident in Gaussian fitting curves. Photoluminescence spectroscopy revealed an augmented emission intensity, likely attributed to increased defect initiation in the Co-doped specimen. Moreover, Raman spectroscopy was employed to identify vibration modes in the examined samples, demonstrating shifts in Raman peaks indicative of Co substitution and subsequent distortion in the crystal structure of YbFeO3. Electrical assessments were conducted at room temperature (300 K) under ambient conditions, employing voltage and frequency as variables. Capacitance–voltage measurements illustrated the emergence of an accumulation, with depletion and inversion regions manifesting at different frequencies based on the applied voltage, attributed to the YbFeO3 interfacial layer at the Al and p-Si interface. The conductance-voltage characteristics indicated that the structure exhibited maximum conductance in the accumulation region. Series resistance for these configurations was deduced from capacitance-conductance-voltage measurements, indicating a dependence on both bias voltage and frequency. The doping process led to a reduction in capacitance and series resistance, accompanied by an increase in conductance values. After obtaining corrected capacitance and conductance parameters, it became evident that series resistance significantly influences both parameters. Interface state density (Nss), determined through the Hill-Coleman relation demonstrated a decreasing trend with increasing frequency. The pure sample exhibited higher interface state density compared to the Co-doped sample at each frequency, highlighting that the 10% Co-doped YbFeO3 thin film enhances the quality of the metal–semiconductor interface properties compared to the pure contact.

Analysis of interface trap induced ledge in β-Ga2O3 based MOS structures using UV-assisted capacitance–voltage measurements

A ledge feature in the capacitance–voltage (CV) profiles of Ga2O3 MOS (metal–oxide–semiconductor) capacitors is investigated using UV-assisted CV measurements. A model is presented whereby the capacitance ledge is associated with carrier trapping in deep-level states at the Al2O3/Ga2O3 interface. Following UV assisted emptying of interface traps at a constant bias, a voltage ramp toward flatband results in a CV ledge when the trap recombination current becomes equal to the quasi-static sweep charging current. The ledge continues until all the traps below the corresponding pinned surface potential have been filled. Varying the UV energy varies the ledge voltage range and allows a density of states to be determined as a function of energy. A broad interface state peak with maximum density ∼8 × 1012 cm−2 eV−1 for deep trap energies lying between 2.4 and 4.1 eV below the conduction band (CB) edge is extracted. Using the conductance method, the interface trap density is also found to rise toward the CB edge in the range 0.25–0.45 eV below the CB edge, reaching a maximum density of ∼1 × 1012 cm−2 eV−1. Combining these two techniques, an interface trap distribution is estimated for almost the entirety of the bandgap of Ga2O3. This novel technique probes deep interface states where standard methods fail to quantify interface states reliably.

C-V characterization of the trap-rich layer in a novel Double-BOX structure

A new Double-BOX structure is introduced to explore the electrical properties of the trap-rich layer used to enhance the performance of radio frequency Silicon-on-Insulator substrates. Capacitance-voltage (C-V) measurements reveal anomalous behavior with a “shoulder” emerging in the electron accumulation region and a shift towards negative gate voltage in hysteresis. TCAD simulation shows that these features are related to trap states at the grain boundary in the trap-rich polycrystalline silicon (polysilicon) layer. These traps form a potential barrier and affect the C-V curves. To determine the traps density in polysilicon, a three-element circuit model is used. The effective density of fast traps is evaluated from the corrected C-V curve, while the hysteresis of double-sweep C-V measurement yields the slow traps density at the grain boundary in polysilicon.

Effect of films thickness and hydrogen annealing on passivation performance of plasma ALD based Hafnium oxide films

We investigate the silicon surface passivation property of Plasma Atomic Layer Deposited (PALD) hafnium oxide thin films and study its dependence on silicon (Si) doping type, film thickness, and post-deposition annealing conditions. Our results demonstrate that as-deposited HfOx films exhibit poor passivation quality that can be improved by performing post-deposition annealing at 450 °C in hydrogen ambient. We demonstrate that the films can effectively passivate p-Si surfaces as compared to n-Si, where the surface passivation quality of the films improves with increasing film thickness for both silicon doping types. The best performance with a minority carrier lifetime of 1.7 ms, corresponding surface recombination velocity (SRV) ∼10 cm s−1, is achieved for HfOx films thickness ∼23 nm deposited on the p-Si substrate. The Capacitance-Voltage (C–V) measurements give an insight into the passivation mechanism of the studied films. Field effect passivation is found to be an important passivation mechanism in PALD-deposited HfOx films, as revealed by C–V measurements. The films are also characterized using Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS), which reveals the chemical passivation provided by hydrogen ambient annealing. Overall, the impact of hafnium oxide film thickness and hydrogen ambient annealing conditions on silicon surface passivation is investigated. Our findings will help in utilizing plasma ALD process based HfOx films for silicon solar cell device application.

Effect of substrate temperature on growth mechanism and properties of PEALD-MgO dielectric films for amorphous-IGZO TFTs

Magnesium oxide (MgO) films have been prepared by plasma enhanced atomic layer deposition with bis(cyclopentadienyl)magnesium precursor and oxygen plasma reactant at substrate temperature between 150 °C and 450 °C. The structural, morphological, optical, and chemical properties of the prepared MgO films were studied by spectroscopic ellipsometer, grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS). The electrical property of MgO film was obtained by performing capacitance-voltage measurement on the Al/MgO/Si structures. The experiment result shows that growth rate of MgO film decreases with the deposition temperature increased. GIXRD analysis presented that MgO films are cubic with predominantly (220) crystal orientation. XPS analysis shows that ratio of Mg/O is highest in MgO film prepared at 350 °C. To illustrate the possible applications of MgO film as a gate dielectric in thin film transistor (TFT), indium‑gallium‑zinc oxide (IGZO) was used as channel layer. The optimized IGZO/MgO TFT showed an electron mobility of 1.63 cm2/Vs, an on/off current ratio of 106, and a subthreshold swing of 0.50 V/decade at a low operation voltage of −0.11 V.

Optical and electronic properties of MgPc-Ch-diisoQ blend organic thin film as an active layer for photovoltaic cells.

Organic photovoltaic cells are a promising technology for generating renewable energy from sunlight. These cells are made from organic materials, such as polymers or small molecules, and can be lightweight, flexible, and low-cost. Here, we have created a novel mixture of magnesium phthalocyanine (MgPc) and chlorophenyl ethyl diisoquinoline (Ch-diisoQ). A coating unit has been utilized in preparing MgPc, Ch-diisoQ, and MgPc-Ch-diisoQ films onto to FTO substrate. The MgPc-Ch-diisoQ film has a spherical and homogeneous surface morphology with a grain size of 15.9 nm. The optical absorption of the MgPc-Ch-diisoQ film was measured, and three distinct bands were observed at 800-600 nm, 600-400 nm, and 400-250 nm, with a band gap energy of 1.58 eV. The current density-voltage and capacitance-voltage measurements were performed to analyze the photoelectric properties of the three tested cells. The forward current density obtained from our investigated blend cell is more significant than that for each material by about 22%. The photovoltaic parameters (Voc, Isc, and FF) of the MgPc-Ch-diisoQ cell were found to be 0.45 V, 2.12 μA, and 0.4, respectively. We believe that our investigated MgPc-Ch-diisoQ film will be a promising active layer in organic solar cells.

High performance of Ag/AlN/Si Schottky diode: Study of the DC sputtering power effect on its electrical properties

The DC sputtering power (DCSP) effect on the chemical composition, structural and electrical properties of Ag/AlN/Si Schottky diode was studied. The AlN films grown on Si substrate were examined by X-ray diffraction (XRD), Fourier Transformed Infra-Red (FTIR), and Raman spectroscopy. The analyzes by XRD, FTIR and Raman show stability at the level of the structure and the qualitative chemical composition of the AlN layer for DCSP of 200 W and 400 W. However, the quantity of chemical compounds on the surface of AlN is affected by this variation. From Current-Voltage (I-V) measurements, the ideality factor (n), barrier height (φb), and series resistance (Rs) were extracted by adopting Cheung functions. Diodes with an AlN interlayer elaborated at 400 W have good rectifying behavior with n, Rs and φb of 3.11, 1930 Ω, and 0.93 eV, respectively. The enhancement of the Ag/AlN/Si diode performance was attributed to the reduction of undesirable impurities in the Ag/AlN interface as well as the morphological improvement of the AlN layer. Capacitance-Voltage (C-V) measurements showed that carrier donor concentrations are strongly affected by DC sputtering power. The elaborate structures may provide new materials with electrical properties having a wide range of applications in electronics and photovoltaic field.

Data-Driven Analysis of High-Resolution Hyperspectral Image Data Sets through Nanoscale Capacitance–Voltage Measurements to Visualize Ferroelectric Domain Dynamics

Data-Driven Analysis of High-Resolution Hyperspectral Image Data Sets through Nanoscale Capacitance–Voltage Measurements to Visualize Ferroelectric Domain Dynamics

Photoelectrical characterization of heavily doped p-SiC Schottky contacts

The availability of photoelectrical characterizations of heavily Al-doped p-SiC Schottky contacts was clarified. We conducted a systematic study of four samples with different Al doping concentrations from 1 × 1018 to 5 × 1019 cm−3. Although the current–voltage (I–V) characteristics had lost rectification, reasonable Schottky barrier height (qϕ B) values were obtained up to 1 × 1019 cm−3 by capacitance voltage, photo response, and scanning internal photoemission microscopy (SIPM) measurements. In the two-dimensional characterization by SIPM, large photocurrent spots corresponding with low qϕ B were observed in an average density of 103 to 104 cm−2. However, except for these spots, a high uniformity of about 2 meV standard deviation was obtained for qϕ B over the entire observed electrodes. These results indicate that SIPM is able to characterize the inhomogeneity of heavily doped p-SiC contacts with very leaky I–V characteristics.