Capacitance behavior of GaAs-MIS structures with low-temperature grown GaAs dielectric

Low temperature (LT-) grown GaAs has been used as a dielectric in a metal/ dielectric/semiconductor structure, and its capacitance behavior has been investigated by C–V_B} and admittance spectroscopy. The C-V_B} measurement revealed a barrier height of 0.40 eV at the interface of the LT- and n-GaAs. The capacitance-temperature profile shows a step decrease in capacitance, accompanied by a maximum conductance as the measurement temperature was decreased. The detailed investigation shows that this anomalous C–T behavior is caused by the increase of resistivity of the LT-GaAs, which leads to the formation of a metal/insulator/semiconductor structure at low temperature. This result has an impact on the application of the LT-GaAs, because it introduces a frequency dispersion to the device characteristics.     

Frequency and voltage dependence of negative capacitance in Au/SiO2/n-GaAs structures

The frequency (f) and bias voltage (V) dependence of electrical and dielectric properties of Au/SiO₂/n-GaAs structures have been investigated in the frequency range of 10 kHz–3 MHz at room temperature by considering the presence of series resistance (R_s). The values of R_s, dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tan δ) of these structures were obtained from capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements and these parameters were found to be strong functions of frequency and bias voltage. In the forward bias region, C–V plots show a negative capacitance (NC) behavior, hence ε′–V plots for each frequency value take negative values as well. Such negative values of C correspond to the maximum of the conductance (G/ω). The crosssection of the C–V plots appears as an abnormality when compared to the conventional behavior of ideal Schottky barrier diode (SBD), metal–insulator–semiconductor (MIS) and metal–oxide–semiconductor (MOS) structures. Such behavior of C and ε′ has been explained with the minority-carrier injection and relaxation theory. Experimental results show that the dielectric properties of these structures are quite sensitive to frequency and applied bias voltage especially at low frequencies because of continuous density distribution of interface states and their relaxation time.     

Frequency and voltage dependence of admittance characteristics of Al/Al2O3/PVA:n-ZnSe Schottky barrier diodes

This paper reports the frequency dependence of admittance measurements i.e C–V and G/ω–V characteristics of Al/Al₂O₃/PVA:n-ZnSe MIS diode. The interface states (N_ss) and series resistance (R_s) of the MIS diode strongly influence the C–V–f and G/ω–V–f characteristics. The conductance method is used to calculate the series resistance (R_s), the density of states (N_ss), insulator layer capacitance and thickness. The frequency dependent dieclectric parameters such as dielectric constant (εʹ), dielectric loss (ε″), loss tangent (tan δ) and a.c. electrical conductivity (σ_ac) has been calculated and which are also responsible for observed frequency dispersion in C–V and G/ω curves.     

Low frequency noise in gate and drain of PHEMT’s and related correlation

Low frequency noise investigations have been carried out in GaAs based psuedomorphic high electron mobility in order to model the up-converted noise in nonlinear applications of these devices. Gate and channel noises are studied versus frequency and versus device biases. The results are analysed with an equivalent circuit issued from conduction investigations. Correlation between input and output noises is also measured. For V_GS<0 V, the main origin of the coherence is located between gate and drain, whereas for V_DS>0 V, the access source resistance must be taken into account.     

Investigations on electrical characteristics and reliability properties of MOS capacitors using HfAlOx on n-GaAs substrates

Radio frequency sputtering system is employed to fabricate metal oxide semiconductor (MOS) capacitors using an ultra-thin layer of HfAlO_x dielectric deposited on n-GaAs substrates with and without a Si interface control layer incorporated in between the dielectric and the semiconductor. Measurements are performed to obtain capacitance voltage (C–V) and current voltage (I–V) characteristics for GaAs/Si/HfAlO_x and GaAs/HfAlO_x capacitors under different constant voltage and constant current stress conditions. The variation of different electrical parameters such as change in interface trap density, hysteresis voltage with various values of constant voltage stress and the dependence of flat band voltage, fractional change in gate leakage current density, etc. with stress time are extracted from the C–V and I–V data for capacitors with and without a Si interlayer. Further the trap charge density and the movement of trap centroid are investigated for various injected influences. The dielectric breakdown and reliability properties of the dielectric films are studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t_bd ? 1350 s) is observed for HfAlO_x gate dielectric with a silicon inter-layer under the high constant voltage stress at 8 V. Compared to capacitors without a Si interlayer, MOS capacitors with a Si interlayer exhibit improved electrical and breakdown characteristics, and excellent interface and reliability properties.     

Dielectric properties in Au/SnO2/n-Si (MOS) structures irradiated under Co-γ rays

The metal-oxide-semiconductor (MOS) structures with insulator layer thickness range of 55-430 Å were stressed with a bias of 0 V during ⁶⁰Co-γ ray source irradiation with the dose rate of 2.12 kGy/h and the total dose range was 0-5×10⁵ Gy. The real part of dielectric constant ε′, dielectric loss ε″, dielectric loss tangent tanδ and the dc conductivity σ_dc were determined from against frequency, applied voltage, dose rate and thickness of insulator layer at room temperature for Au/SnO₂/n-Si (MOS) structures from C-V capacitance and G-V conductance measurements in depletion and weak inversion before and after irradiation. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. The frequency, applied voltage, dose rate and thickness dependence of ε′, ε″, tanδ and σ_dc are studied in the frequency (500 Hz-10 MHz), applied voltage (−10 to 10 V), dose rate (0-500 kGy) and thickness of insulator layer (55-430 Å) range, respectively. In general, dielectric constant ε′, dielectric loss ε″ and dielectric loss tangent are found to decrease with increasing the frequency while σ_dc is increased. Experimental results shows that the interfacial polarization can be more easily occurred at the lower frequency and/or with the number of density of interface states between Si/SnO₂ interfaces, consequently, contribute to the improvement of dielectric properties of Au/SnO₂/n-Si (MOS) structures.     

Correlation between thermal resistance, channel temperature, infrared thermal maps and failure mechanisms in low power MESFET devices

Channel temperature T_ch of GaAs MESFETs, determined by means of electrical measurements (ΔV_gs), has been compared and correlated with thermal maps obtained by high resolution infrared microscopy. Results show that in low power devices with a small number of gates, the value of T_ch derived from ΔV_gs measurements is close to the maximum values of temperature measured on the hottest junctions on the chip. Local thermal inhomogeneities, in particular those observed in devices characterized by high values of R_th, can explain and confirm results of failure analyses of MESFETs submitted to accelerated life tests in operating conditions where degradation phenomena occur in localized areas of the device.     

RF power performance evaluation of surface channel diamond MESFETs

We experimentally investigate the large-signal radio frequency performances of surface-channel p-type diamond MESFETs fabricated on hydrogenated polycrystalline diamond. The devices under examination have a coplanar layout with two gate fingers, total gate periphery of 100 μm; in DC they exhibit a hole accumulation behavior with threshold voltage V_t ≈ 0-0.5 V and maximum drain current density of 120 mA/mm. The best small-signal radio frequency performances (maximum cutoff or transition frequency f_T and oscillation frequency f_max) were obtained close to the threshold and were of the order of 6 and 15 GHz, respectively. The power radio frequency response was characterized by driving the devices in class A at an operating frequency of 2 GHz and identifying through the active load-pull technique the optimum load for maximum power added efficiency. A power gain in linearity of 8 dB and an output power of approximately 0.2 W/mm with 22% power added efficiency were obtained on the optimum load impedance at a bias point V_DS = −14 V, V_GS = −1 V. To the best of our knowledge, these are the first large signal measurements ever reported for surface MESFET on polycrystalline diamond, and show the potential of such technology for the development of microwave power devices.     

GaAs-based metal-oxide semiconductor field-effect transistors with Al2O3 gate dielectrics grown by atomic layer deposition

We demonstrate GaAs-based, metal-oxide-semiconductor field-effect transistors (MOSFETs) with excellent performance using an Al₂O₃ gate dielectric, deposited by atomic layer deposition (ALD). This achievement is very significant because Al₂O₃ possesses highly desirable physical and electrical properties as a gate dielectric. These MOSFET devices exhibit extremely low gate-leakage current, high transconductance, and high dielectric breakdown strength. A short-circuit, current-gain, cutoff frequency (f_T) of 14 GHz and a maximum oscillation frequency (f_max) of 25.2 GHz have been achieved from a 0.65-μm gate-length device. The interface trap density (D_it) of Al₂O₃/GaAs is evaluated by the hysteresis of drain-source current, I_ds, versus gate-source bias, V_gs, and the frequency dispersion of transconductance, g_m.     

Comparison of Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films Grown on (100) LaAlO3 and (100) MgO Single-Crystal Substrates

The microwave properties of barium strontium titanate (Ba_0.6Sr_0.4TiO₃) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single-crystal substrates through the sol–gel technique were investigated. The interdigital capacitor (IDC) technique was used to measure the nonlinear dielectric properties in the frequency range from 1 GHz to 10 GHz. The results show that the Curie temperature, capacitance, and tunability of the films are strongly dependent upon the substrate. The film fabricated on the LaAlO₃ substrate has a higher tunability of 16.77% than that grown on the MgO substrate (～8.38%), measured at 10 GHz with an applied voltage of 35 V. The loss tangent is a linear function of the frequency in the microwave range, and the film grown on the MgO substrate has a lower loss tangent than that grown on the LAO substrate. This work reveals the great potential of Ba_0.6Sr_0.4TiO₃ (BST) films for application in tunable microwave devices.     

Dielectric relaxation contribution to dispersion of junction admittance

Significant frequency dispersion is observed in capacitance vs voltage measurements on solar cell structures prepared on high resistivity semiconductors such as a-Si and CdS. An equivalent circuit analysis of both Schottky barrier and Mott barrier devices shows that the equivalent parallel plate capacitance measured in an experiment corresponds to the distance from the interface to a position in the semiconductor bulk where the dielectric relaxation time is $\text{τ(x}{}_1\text{) =}\text{1}\text{ω}$ with ω the angular frequency. Comparison of measured C - V - f curves with reported for junctions in the dark and under $\text{～}\text{1}\text{3}$ AM1 illumination.     

An improved GaAs device model for the simulation of analog integrated circuit

This paper describes an improved device model of GaAs MESFETs and heterojunction FETs for the design and analysis of analog integrated circuits. The proposed device model provides a new expression for the current and the capacitance of the device,which gives excellent agreements with experimental data for all regions of device operation. For the expression of the low frequency anomalies of GaAs devices, an improved technique with an equivalent circuit are presented to model the frequency dispersion of the transconductance and the drain conductance of the device, which give a good agreement with the experimental data of both the frequency dispersion and the lag effect of the device. The new device model proposed here clearly provides a superior prediction of the performance of GaAs analog integrated circuit.     

Electrical measurements of voltage stressed Al2O3/GaAs MOSFET

Electrical characteristics of GaAs metal–oxide–semiconductor field effect transistor with atomic layer deposition deposited Al₂O₃ gate dielectric have been investigated. The IV characteristics were studied after various constant voltage stress (CVS) has been applied. A power law dependence of the gate leakage current (I_g) on the gate voltage (V_g) was found to fit the CVS data of the low positive V_g range. The percolation model well explains the degradation of I_g after a high positive V_g stress. A positive threshold voltage (V_th) shift for both +1.5 V and +2 V CVS was observed. Our data indicated that positive mobile charges may be first removed from the Al₂O₃ layer during the initial CVS, while the trapping of electrons by existing traps in the Al₂O₃ layer is responsible for the V_th shift during the subsequent CVS.     

Temperature and frequency dependent electrical and dielectric properties of Al/SiO2/p-Si (MOS) structure

The electrical and dielectric properties of Al/SiO₂/p-Si (MOS) structures were studied in the frequency range 10 kHz-10 MHz and in the temperature range 295-400 K. The interfacial oxide layer thickness of 320 Å between metal and semiconductor was calculated from the measurement of the oxide capacitance in the strong accumulation region. The frequency and temperature dependence of dielectric constant (ε′), dielectric loss (ε″), dielectric loss tangent (tan δ) and the ac electrical conductivity (σ_ac) are studied for Al/SiO₂/p-Si (MOS) structure. The electrical and dielectric properties of MOS structure were calculated from C-V and G-V measurements. Experimental results show that the ε′ and ε″ are found to decrease with increasing frequency while σ_ac is increased, and ε′, ε″, tan δ and σ_ac increase with increasing temperature. The values of ε′, ε″ and tan δ at 100 kHz were found to be 2.76, 0.17 and 0.06, respectively. The interfacial polarization can be more easily occurred at low frequencies, and the number of interface state density between Si/SiO₂ interface, consequently, contributes to the improvement of dielectric properties of Al/SiO₂/p-Si (MOS) structure. Also, the effects of interface state density (N_ss) and series resistance (R_s) of the sample on C-V characteristics are investigated. It was found that both capacitance C and conductance G were quite sensitive to temperature and frequency at relatively high temperatures and low frequencies, and the N_ss and R_s decreased with increasing temperature. This is behavior attributed to the thermal restructuring and reordering of the interface. The C-V and G/ω-V characteristics confirmed that the N_ss, R_s and thickness of insulator layer (δ) are important parameters that strongly influence both the electrical and dielectric parameters and conductivity in MOS structures.     

⟨110⟩-oriented GaAs MESFETs

GaAs metal semiconductor field-effect transistors (MESFETs) have been successfully fabricated on molecular-beam epitaxial (MBE) films grown on the off-axis (110) GaAs substrate. The (110) substrates were tilted 6° toward the (111) Ga face in order to produce device quality two-dimensional MBE growth. Following the growth of a 0.4-μm undoped GaAs buffer, a 0.18-μm GaAs channel with a doping density of 3.4×10¹⁷ cm^-3 and a 0.12-μm contact layer with a doping density of 2×10¹⁸ cm^-3, both doped with Si, were grown. MESFET devices fabricated on this material show very low-gate leakage current, low output conductance, and an extrinsic transconductance of 200 mS/mm. A unity-current-gain cutoff frequency of 23 GHz and a maximum frequency of oscillation of 56 GHz have been achieved. These (110) GaAs MESFETs have demonstrated their potential for high-speed digital circuits as well as microwave power FET applications     

Oscillations in Ballistic FETs

Oscillation processes in V-shaped-gate GaAs MESFETs with the effective channel length 30 nm is discussed. The transistors were made by electron lithography and anisotropic etching to shape the gate. The analytic transit time of electrons along the channel was found to be less than 0.1 ps. The oscillation frequency varied from 30 to 37 GHz. It is shown that a decrease in the gate–source capacitance affects the oscillating signal only slightly. Unlike Gunn diodes, neutron irradiation has an insignificant effect on the signal up to fluences of 10¹⁵ cm^–2. The exposure to IR radiation may change the signal amplitude twofold, with the oscillation frequency being changed by less than 0.1%.     

Temperature dependent electrical and dielectric properties of Au/polyvinyl alcohol (Ni, Zn-doped)/n-Si Schottky diodes

The electrical and dielectric properties of Au/PVA (Ni, Zn-doped)/n-Si Schottky diodes (SDs) were studied in the temperature range of 80-400 K. The investigation of various SDs fabricated with different types of interfacial layer is important for understanding the electrical and dielectric properties of SDs. Therefore, in this study polyvinyl alcohol (PVA) film was used as an interfacial layer between metal and semiconductor. The electrical and dielectric properties of Au/PVA (Ni, Zn-doped)/n-Si SDs were calculated from the capacitance-voltage (C-V) and conductance-voltage (G/w-V) measurements. The effects of interface state density (N_ss) and series resistance (R_s) on C-V characteristics were investigated in the wide temperature range. It was found that both of the C-V-T and G/w-V-T curves included two abnormal regions and one intersection point. The dielectric constant (ε″), dielectric loss (ε″), dielectric loss tangent (tan δ) and the ac electrical conductivity (σ_ac) obtained from the measured capacitance and conductance were studied for Au/PVA (Ni, Zn-doped)/n-Si SDs. Experimental results show that the values of ε′, ε″ and tan δ are a strong function of the temperature. Also, the results indicate the interfacial polarization can be more easily occurred at high temperatures.     

Integration of high-Q GaAs varactor diodes and 0.25 μmGaAs MESFET's for multifunction millimeter-wave monolithic circuitapplications

Two technologies are demonstrated whereby high-Q, vertical-structure, abrupt-junction varactor diodes are monolithically integrated with 0.25-μm GaAs MESFETs on semi-insulating GaAs substrates for multifunction millimeter-wave monolithic circuit applications. Diodes with various anode sizes have been realized with measured capacitance swings of >2.1:1 from 0 V to -4 V and series resistances of approximately 1 Ω. Diodes having a zero bias capacitance of 0.35 pF have Q's of >19000 (50 MHz) with -4 V applied to the anode. Under power bias conditions, the MESFETs have a measured gain of >6 dB at 35 GHz with extrapolated values for f _t and f_max of 32 GHz and 78 GHz, respectively. Using these technologies, a monolithic Ka-band voltage controlled oscillator (VCO) containing a varactor diode, a 0.25-μm GaAs MESFET, and the usual MMIC passive components has been built and tested. At around 31 GHz, the circuit has demonstrated 60-mW power output with 300 MHz of tuning bandwidth     

Temperature dependent electrical and dielectric properties of a metal/Dy2O3/n-GaAs (MOS) structure

This paper describes the structural properties, electrical and dielectric characteristics of thin Dy₂O₃ layer deposited on the n-GaAs substrate by electron beam deposition under ultra vacuum. Structural and morphological characterizations are investigated by atomic force microscopy (AFM) and X-ray diffraction measurements (XRD). The XRD shows that the elaborated Dy₂O₃ oxide has a cubic structure. The electrical and dielectric properties of Co/Au/Dy₂O₃/n-GaAs structure were studied in the temperature range of 80–500 K. The conductance and capacitance measurements were performed as a function of bias voltage and frequency. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) of the structure are obtained from capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. These parameters are found to be strong functions of temperature and bias voltage. A strong negative capacitance (NC) phenomenon has been observed in C–V; hence ε′–V plots for each temperature value take negative values. The following behavior of the C and ε′ in the forward bias region has been explained with the minority-carrier injection and relaxation theory. From DC conductance study, electronic conduction is found to be dominated by thermally activated hopping at high temperature. Activation energy is deduced from the variation of conductance with temperature. The interface state density (N_ss) of the structure is of the order 1.13×10¹³ eV⁻¹ cm⁻².     

钝化介质层对功率GaAs MESFET的栅-漏击穿特性影响

用直接测定GaAs MESFET的栅-漏极电容-频率（C-f)和高频电容—电压（C-V）的方法,研究了钝化层—半导体界面的慢界面陷阱电荷对栅—漏反向击穿特性的影响,为解决GaAs MESFET的栅—漏反向击穿特性不良和不稳定提供了依据。