Lingguo Meng

Polarization Coulomb field scattering in AlGaN/AlN/GaN heterostructure field-effect transistors

Using the measured capacitance-voltage curves of Ni Schottky contacts with different contact areas and the current-voltage characteristics for the circular and rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) at low drain-source voltage, we found that the polarization Coulomb field scattering has an important influence on the two-dimensional electron gas (2DEG) electron mobility in both the circular and rectangular AlGaN/AlN/GaN HFETs. Moreover, the polarization Coulomb field scattering in AlGaN/AlN/GaN heterostructures is relatively weaker compared to that in AlGaN/GaN heterostructures, which is attributed to the AlN interlayer in AlGaN/AlN/GaN heterostructures to enlarge the average distance between the 2DEG electrons and the polarization charges.

Extraction of AlGaN/GaN heterostructure Schottky diode barrier heights from forward current-voltage characteristics

Ni Schottky contacts on AlGaN/GaN heterostructures have been fabricated, and one of the prepared samples has been annealed at 700 °C for half an hour. The barrier heights for the prepared samples were measured by internal photoemission. Based on the measured forward current-voltage (I-V) characteristics and using the two-diode model, the Ni Schottky barrier height at zero bias has been analyzed and calculated by self-consistently solving Schrodinger’s and Poisson’s equations, and the correlation expression between the barrier height at zero electric field and that at zero bias has been derived for Schottky contacts on AlGaN/GaN heterostructures. The calculated Schottky barrier heights corresponding to zero electric field for the prepared Ni Schottky contacts on AlGaN/GaN heterostructures agree well with the photocurrent measured results. Thus, the method for extraction of AlGaN/GaN heterostructure Schottky barrier heights from forward I-V characteristics is developed and determined.

Influence of the side-Ohmic contact processing on the polarization Coulomb field scattering in AlGaN/AlN/GaN heterostructure field-effect transistors

Using the measured capacitance-voltage curves of Ni Schottky contacts with different areas and the current-voltage characteristics for the circular and rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with the side-Ohmic contacts, it is found that the polarization Coulomb field scattering caused by the polarization charge density variation at the AlGaN/AlN/GaN interfaces is closely related to the Ohmic-contact processing, and the side-Ohmic contact processing greatly weakens the polarization Coulomb field scattering in the AlGaN/AlN/GaN HFETs.

Evaluating AlGaN/AlN/GaN heterostructure Schottky barrier heights with flat-band voltage from forward current-voltage characteristics

Both circular and rectangular Ni Schottky contacts on AlGaN/AlN/GaN heterostructures have been fabricated. Both of the Schottky barrier heights were measured by internal photoemission. The flat-band voltage (V0) for the AlGaN/AlN/GaN heterostructure Schottky contacts was analyzed and obtained from the forward current-voltage (I-V) characteristics. Based on the forward I-V characteristics and with the obtained flat-band voltage, the Schottky barrier heights for the circular and rectangular diodes have been analyzed and calculated by self-consistently solving Schrodinger’s and Poisson’s equations. The evaluated Schottky barrier heights for the prepared circular and rectangular Ni Schottky diodes agree well with the photocurrent measured results.

Influence of the ratio of gate length to drain-to-source distance on the electron mobility in AlGaN/AlN/GaN heterostructure field-effect transistors

Using measured capacitance-voltage curves with different gate lengths and current–voltage characteristics at low drain-to-source voltage for the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) of different drain-to-source distances, we found that the dominant scattering mechanism in AlGaN/AlN/GaN HFETs is determined by the ratio of gate length to drain-to-source distance. For devices with small ratio (here, less than 1/2), polarization Coulomb field scattering dominates electron mobility. However, for devices with large ratio (here, more than 1/2), longitudinal optical (LO) phonon scattering and interface roughness scattering are dominant. The reason is closely related to polarization Coulomb field scattering.

Energy Recovery Circuit with Auxiliary Power Supply for AC Plasma Display Panel

A new energy recovery circuit with an auxiliary power supply for AC plasma display panel is proposed, which can provide zero-voltage switching of all switches by rejecting the surge current when sustain switches are turned on. The operation process of the circuit is analyzed, and the results of experiments based on a 12-in PDP panel with 100 kHz sustaining frequency show that the proposed circuit could reduce power losses of energy recovery circuit of AC plasma display panel.

Polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors

Using the measured capacitance-voltage curves of Ni Schottky contacts with different areas and the current-voltage characteristics for the rectangular and circular In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors (HFETs) at low drain-source voltage, we found that the Ohmic contact processing and the gate bias cause the irregular distribution of the polarization charges at the In0.18Al0.82N/AlN interface which generates the polarization Coulomb field, and the polarization Coulomb field scattering has an important influence on the two-dimensional electron gas electron mobility in both our rectangular and circular In0.18Al0.82N/AlN/GaN HFET devices as same as in AlGaN/AlN/GaN HFET devices.

A Line Array of Microplasma Devices With Coplanar Electrodes Operating in Argon

A line array of microplasma devices with coplanar electrodes has been fabricated, and the discharge characteristics of the microplasma devices under different argon pressures were investigated in experiments which were driven by sinusoidal voltage and alternating pulse voltage, respectively. The microcavities of the proposed device are composed of two coplanar electrodes instead of dielectric or single cathode. The voltage-current characteristics of the device driven by sinusoidal voltage show that the power loading of each microcavity could reach several kilowatts per cubic centimeter. Driven by alternating pulse voltage, the device performed a trend that the discharge current grows up first and then goes down gradually with the increase of operation pressure. Moreover, with the increase of driven frequency, the device operated with high discharge stability on both time and intensity. The proposed device possesses the advantages of simple structure and simple fabrication processes.

A simple method of extracting the polarization charge density in the AlGaN/GaN heterostructure from current-voltage and capacitance-voltage characteristics

An Ni Schottky contact on the AlGaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the AlGaN/GaN heterostructure is obtained from the forward current—voltage characteristics. With the measured capacitance—voltage curve and the flat-band voltage, the polarization charge density in the AlGaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodingers and Poissons equations.

Simulations of Breakdown Voltage of Coplanar Electrodes Microplasma Devices

Microplasmas have attracted more and more attention due to their unique characteristics, and breakdown voltage is an important parameter for microplasma devices, particularly for addressable arrays of microplasma devices. However, small changes in shape or interface would bring obvious change in breakdown voltage. In this paper, five groups of simulations of breakdown voltage were operated under different geometry parameters to develop the trend of breakdown voltage following geometrical size under different operation pressures. The drift-diffusion approximation model is adopted in these simulations. The simulation results show that breakdown voltage will increase with the increase in the microcavity depth and thickness of the dielectric. Therefore, the breakdown voltage will reduce when microcavity width increases. The less is the microcavity size, the less is breakdown voltage, and the higher is the pressure corresponding to minimum breakdown voltage, which shows that the decrease in microcavity size can develop operation pressure and decrease breakdown voltage obviously.