다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Trapping is one of the most deleterious effects that limit performance and reliability in GaN HEMTs. In this paper, we present a methodology to study trapping characteristics in GaN HEMTs that is based on current-transient measurements. Its uniqueness is that it is amenable to integration with electrical stress experiments in long-term reliability studies. We present the details of the measurement and analysis procedures. With this method, we have investigated the trapping and detrapping dynamics of GaN HEMTs. In particular, we examined layer location, energy level, and trapping/detrapping time constants of dominant traps. We have identified several traps inside the AlGaN barrier layer or at the surface close to the gate edge and in the GaN buffer.

http://www.mtl.mit.edu/~alamo/pdf/2011/RJ-128.pdf

A Current-Transient Methodology for Trap Analysis for GaN High Electron Mobility Transistors

We propose a modified droplet epitaxy method for fabricating self-organized GaAs/AlGaAs quantum dots (QDs) with a high As flux irradiation and a low substrate temperature. By our novel method, GaAs QDs were successfully formed, retaining their pyramidal shape, original base size and density of droplets, and preventing layer-by-layer growth. Quantum size effects of the QDs were distinctly observed by photoluminescence measurements. It was confirmed that this new modified droplet epitaxy method is promising for fabricating a high-quality GaAs/AlGaAs QD system.

https://iopscience.iop.org/article/10.1143/JJAP.39.L79/pdf

Fabrication of GaAs Quantum Dots by Modified Droplet Epitaxy

The potential modulation and interface states of Al2O3/Al0.25Ga0.75N/GaN structures prepared by atomic layer deposition (ALD) were characterized by capacitance–voltage (C–V) measurements. We observed the peculiar C–V characteristics with two capacitance steps in forward and reverse bias regions, corresponding to the electron accumulation or depletion behavior at the Al2O3/AlGaN and AlGaN/GaN interfaces. From the experimental and calculated C–V characteristics, it was found that the charging and discharging of interface states near the AlGaN conduction-band edge mainly caused the stretch-out and hysteresis of the C–V curve at the forward bias. On the other hand, it is likely that the interface states near the midgap or deeper in energies act as fixed charges. From the bias-dependent hysteresis voltage in the forward bias region and the photo-induced voltage shift at the reverse bias, we estimated the interface state density distribution at the Al2O3/AlGaN interface for the first time. The present ALD-Al2O3/AlGaN/GaN structure showed relatively high interface state densities with a minimum density of 1×1012 cm-2 eV-1 or higher.

https://iopscience.iop.org/article/10.1143/JJAP.50.021001/pdf

Capacitance?Voltage Characteristics of Al2O3/AlGaN/GaN Structures and State Density Distribution at Al2O3/AlGaN Interface

III-V semiconductors, GaAs and in particular InGaP, are used in many different electronic applications, such as high power and high frequency devices, laser diodes and high brightness LED. Their direct bandgap and high reliability make them ideal candidates for the realisation of high efficiency solar cells: in the past years they have been successfully used as power sources for satellites in space, where they are able to produce electricity from sunlight with an overall efficiency of around 30%. Nowadays, the use of arsenides and phosphides as photovoltaic (PV) devices is confined only to space applications since their price is much higher than conventional Si flat panel modules, the leading PV market technology. But with the introduction of multijunction solar cells capable of operating in high concentration solar light, the area and, therefore, the cost of these cells can be reduced and will eventually find an application and market also on Earth. This article will review the situation of semiconductor solar cell materials, focusing on Si, GaAs, InGaP and multijunction solar cells and will discuss future trends and possibilities of bringing III-V technology from space to Earth. Copyright © 2006 John Wiley & Sons, Ltd.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.715

The potential of III-V semiconductors as terrestrial photovoltaic devices

We report on frequency dependent capacitance and conductance analysis of the AlGaN/GaN/Si heterostructure field-effect transistors (HFETs) and Al2O3/AlGaN/GaN/Si metal-oxide-semiconductor HFETs (MOSHFETs) in order to investigate the trap effects in these devices. The capacitance of the HFETs exhibits significantly higher frequency dispersion than that of the MOSHFETs. Two different types of traps were found from the conductance analysis on both types of devices, fast with the time constant τ≅(0.1–1) μs and slow with τ=8 ms. The density of trap states evaluated on the HFETs was DT≅2.5×1012 and up to 1013 cm−2 eV−1 for the fast and slow traps, respectively. Analysis of the MOSHFETs yielded only slightly lower DT of the fast traps (≅1.5×1012 cm−2 eV−1), but nearly two orders of magnitude lower density of slow traps (≤4×1011 cm−2 eV−1) than those of the HFETs. This indicates an effective passivation of slow surface related traps but less influence on fast (probably bulk related) trapping states by applying an insulator on the AlGaN/GaN HFET.

Investigation of trapping effects in AlGaN/GaN/Si field-effect transistors by frequency dependent capacitance and conductance analysis

The authors report on improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). It is found that the drift mobility in the MOSHFET structures with 4nm thick Al2O3 gate oxide is significantly higher than that in HFETs. The zero-bias mobilities are 1950 and 1630cm2∕Vs for the MOSHFET and HFET, respectively. An ∼40% increase of the saturation drain current in the MOSHFETs compared to the HFETs seems to be larger than expected from the passivation effects. The MOSHFET devices show a higher transconductance (with peak values of ∼115mS∕mm) than the HFETs (∼70mS∕mm). Analysis of the device performance indicates a decrease of the parasitic series resistance together with an enhancement of the effective velocity of the channel electrons in the MOSHFET devices.

Improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistor

We report on the frequency dependent conductance measurements of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). The properties of the devices with as-deposited and annealed 9-nm-thick Al2O3 gate oxide were investigated. The trap density in the range of 1011 cm−2 eV−1 was evaluated for the nonannealed devices. However, the conductance versus frequency peaks were significantly broader than those expected from theory, which indicates a surface potential fluctuation due to nonuniformities in the oxide charge and interface traps. Additionally, the dependence of the trap state time constant on gate voltage showed a deviation from the expected exponential function. However, the annealed devices (680 °C, 5 min) yielded a slightly lower (∼75%) trap density. Moreover, the conductance versus frequency data and the time constant versus gate voltage dependence of the annealed devices were in full agreement with the theoretical ones. The results show that the frequency dependen...

Characterization of AlGaN/GaN metal-oxide-semiconductor field-effect transistors by frequency dependent conductance analysis

The Al 2 O 3 as a gate oxide and passivation was used to study the transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOSHFETs). Performance of the devices with Al 2 O 3 of different thickness between 4 and 14 nm prepared by metal–organic chemical vapor deposition (MOCVD) and with 4 nm thick Al 2 O 3 prepared by Al sputtering and oxidation was investigated. All MOS-devices yielded higher transconductance than their HFET counterparts, i.e. the transconductance/capacitance expected proportionality assuming the same carrier velocity was not fulfilled. A different electric field near/below the gate contact due to a reduction of traps is responsible for the carrier velocity enhancement in the channel of the MOSHFET. The trap reduction depends on the oxide used, as follows from the capacitance vs frequency dispersion for devices investigated. It is qualitatively in a good agreement with the different velocity enhancement evaluated, and devices with thinner oxide show higher traps reduction as well as higher transconductance enhancement. It is also shown that obtained conclusions can be applied well on performance of SiO 2 /AlGaN/GaN MOSHFETs.

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

Atomic layer deposition (ALD) of Al2O3 was used to prepare metal-oxide-semiconductor (MOS) devices on two different_AlGaN/GaN heterostructures, with and without a thin GaN cap layer. Their trapping effects were evaluated by the frequency dependent conductance measurement. The trap state density decreased sharply from ∼1×1012 cm−2 eV−1 at the energy of 0.27 eV to ∼3×1010 cm−2 eV−1 at 0.45 eV. The low trap state density and exactly exponential dependence of the trap state time constant on the gate voltage show a good quality of the gate oxide. The trap state density in the structure with a GaN cap is about 2–3 times lower than that in the structure without a cap, which might be due to the different Al2O3/GaN and Al2O3/AlGaN interface properties. The trap state density in the structures investigated is lower than those reported for the devices with the metal-organic chemical vapor deposition and Al-oxidized Al2O3 gate oxide. This shows an importance of the ALD technique for the preparation of high-performanc...

Jozef Novák

Papers

Investigation of trapping effects in AlGaN/GaN/Si field-effect transistors by frequency dependent capacitance and conductance analysis

Improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistor

Characterization of AlGaN/GaN metal-oxide-semiconductor field-effect transistors by frequency dependent conductance analysis

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

Trap states in AlGaN/GaN metal-oxide-semiconductor structures with Al2O3 prepared by atomic layer deposition