Atomic layer deposited HfO2 based metal insulator semiconductor GaN ultraviolet photodetectors

A report on GaN based metal insulator semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with atomic layer deposited (ALD) 5-nm-thick HfO₂ insulating layer is presented. Very low dark current of 2.24 × 10⁻¹¹ A and increased photo to dark current contrast ratio was achieved at 10 V. It was found that the dark current was drastically reduced by seven orders of magnitude at 10 V compared to samples without HfO₂ insulating layer. The observed decrease in dark current is attributed to the large barrier height which is due to introduction of HfO₂ insulating layer and the calculated barrier height was obtained as 0.95 eV. The peak responsivity of HfO₂ inserted device was 0.44 mA/W at bias voltage of 15 V.     

Evidence of GeO volatilization and its effect on the characteristics of HfO2 grown on Ge substrate

HfO₂ films are deposited by atomic layer deposition (ALD) using tetrakis ethylmethylamino hafnium (TEMAH) as the hafnium precursor, while O₃ or H₂O is used as the oxygen precursor. After annealing at 500℃ in nitrogen, the thickness of Ge oxide's interfacial layer decreases, and the presence of GeO is observed at the H₂O-based HfO₂ interface due to GeO volatilization, while it is not observed for the O₃-based HfO₂. The difference is attributed to the residue hydroxyl groups or H₂O molecules in H₂O-based HfO₂ hydrolyzing GeO₂ and forming GeO, whereas GeO is only formed by the typical reaction mechanism between GeO₂ and the Ge substrate for O₃-based HfO₂ after annealing. The volatilization of GeO deteriorates the characteristics of the high-κ films after annealing, which has effects on the variation of valence band offset and the C–V characteristics of HfO₂/Ge after annealing. The results are confirmed by X-ray photoelectron spectroscopy (XPS) and electrical measurements.     

Metal carbide-induced negative flatband voltage shift in TaCx and HfCx/HfO2 gate stacks

We systematically investigated the role of the top interface for TaC_x and HfC_x/HfO₂ gate stacks on the effective work function (Φ_m,eff) shift by inserting a SiN layer at the gate/HfO₂ top interface or HfO₂/SiO₂ bottom interface. We found that Φ_m,eff of the TaN gate electrode on HfO₂ was larger than that on SiO₂ because of the HfO₂/SiO₂-bottom-interface dipole. On the other hand, we found that Φ_m,eff values of the TaC_x and HfC_x gate electrodes on HfO₂ agree with Φ_m,eff on SiO₂. This is because the potential offset of the opposite direction with respect to the bottom interface dipole appears at the metal carbide/HfO₂ interface. It is thus concluded that the top interface in the metal carbide/HfO₂ gate stacks causes the negative Φ_m,eff shift.     

An AlGaN/GaN HEMT with enhanced breakdown and near-zero breakdown voltage temperature coefficient

An AlGaN/GaN high-electron mobility transistor (HEMT) with a novel source-connected air-bridge field plate (AFP) is experimentally verified. The device features a metal field plate that jumps from the source over the gate region and lands between the gate and drain. When compared to a similar size HEMT device with conventional field plate (CFP) structure, the AFP not only minimizes the parasitic gate to source capacitance, but also exhibits higher OFF-state breakdown voltage and one order of magnitude lower drain leakage current. In a device with a gate to drain distance of 6 μm and a gate length of 0.8 μm, three times higher forward blocking voltage of 375 V was obtained at V_GS=-5 V. In contrast, a similar sized HEMT with CFP can only achieve a breakdown voltage no higher than 125 V using this process, regardless of device dimensions. Moreover, a temperature coefficient of 0 V/K for the breakdown voltage is observed. However, devices without field plate (no FP) and with optimized conventional field plate (CFP) exhibit breakdown voltage temperature coefficients of -0.113 V/K and -0.065 V/K, respectively.     

Al2O3绝缘层的AlGaN/GaN MOSHEMT器件研究

在研制AlGaN/GaN HEMT器件的基础上,采用ALD法制备了Al₂O₃ AlGaN/GaN MOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al₂O₃薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现：所制备的Al₂O₃薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较 关键词： 2O₃')" href="#">Al₂O₃ ALD GaN MOSHEMT     

An AlGaN/GaN HEMT with reduced surface electric field and improved breakdown voltage

A reduced surface electric field in AlGaN/GaN high electron mobility transistor (HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas (2-DEG) channel as an electric field shaping layer. The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions. Compared with the HEMTs with conventional source-connected field plate and double field plate, the HEMT with Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge. By optimizing both the length of Mg-doped layer, L_m, and the doping concentration, a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure, respectively. In a device with V_GS=-5 V, L_m=1.5 μm, a peak Mg doping concentration of 8× 10¹⁷ cm^-3 and a drift region length of 10 μm, the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

Characteristics improvement of HfO2/Ge gate stack structure by fluorine treatment of germanium surface

Chemical reactivity of fluorine molecule (F₂)-germanium (Ge) surface and dissociation of fluorine (F)-Ge bonding have been simulated by semi-empirical molecular orbital method theoretically, which shows that F on Ge surface is more stable compared to hydrogen. Ge MIS (metal insulator semiconductor) capacitor has been fabricated by using F₂-treated Ge(1 0 0) substrate and HfO₂ film deposited by photo-assisted MOCVD. Interface state density observed as a hump in the C-V curve of HfO₂/Ge gate stack and its C-V hysteresis were decreased by F₂-treatment of Ge surface. XPS (X-ray photoelectron spectroscopy) depth profiling reveals that interfacial layer between HfO₂ and Ge is sub-oxide layer (GeO_x or HfGeO_x), which is believed to be origin of interface state density.F was incorporated into interfacial layer easily by using F₂-treated Ge substrate. These results suggest that interface defect of HfO₂/Ge gate stack structure could be passivated by F effectively.     

Fabrication and characteristics of high-K HfO2 gate dielectrics on n-germanium

This paper reports that the high-K HfO2 gate dielectrics are fabricated on n-germanium substrates by sputtering Hf on Ge and following by a furnace annealing. The impacts of sputtering ambient, annealing ambient and annealing temperature on the electrical properties of high-K HfO2 gate dielectrics on germanium substrates are investigated. Experimental results indicate that high-K HfO2 gate dielectrics on germanium substrates with good electrical characteristics are obtained, the electrical properties of high-K HfO2 gate dielectrics is strongly correlated with sputtering ambient, annealing ambient and annealing temperature.     

Influence of different oxidants on band alignment of HfO2 films deposited by atomic layer deposition

Based on X-ray photoelectron spectroscopy (XPS), influences of different oxidants on band alignment of HfO₂ films deposited by atomic layer deposition (ALD) are investigated in this paper. The measured valence band offset (VBO) value for H₂O-based HfO₂ increases from 3.17 eV to 3.32 eV after annealing, whereas the VBO value for O₃-based HfO₂ decreases from 3.57 eV to 3.46 eV. The research results indicate that the silicate layer changes in different ways for H₂O-based and O₃-based HfO₂ films after annealing process, which plays a key role in generating the internal electric field formed by the dipoles. The variations of the dipoles at the interface between the HfO₂ and SiO₂ after annealing may lead the VBO values of H₂O-based and O₃-based HfO₂ to vary in different ways, which is in agreement with the varition of flat band (V_FB) voltage.     

Effect of O-vacancy defects on the Schottky barrier heights in Ni/SiO2 and Ni/HfO2 interfaces

We perform first-principles density functional calculations to study the electronic structure of Ni/HfO₂ and Ni/SiO₂ interfaces and the effect of O-vacancy (V_O) defects on the Schottky barrier height and the effective work function. We generate two interface models in which Ni is placed on O-terminated HfO₂ (1 0 0) and α-quartz (1 0 0) surfaces. As the concentration of V_O defects at the interface increases, the p-type Schottky barrier height tends to increase in the Ni/HfO₂ interface, due to the reduction of interface dipoles, whereas it is less affected in the Ni/SiO₂ interface.     

具有高开启/关断电流比的Al2O3/AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

采用原子层淀积(ALD)方法,制备了Al₂O₃为栅介质的高性能AlGaN/GaN金属氧化物半导体高电子迁移率晶体管(MOS-HEMT)。在栅压为-20 V时,MOS-HEMT的栅漏电比Schottky-gate HEMT的栅漏电低4个数量级以上。在栅压为+2 V时,Schottky-gate HEMT的栅漏电为191μA;在栅压为+20 V时,MOS-HEMT的栅漏电仅为23.6 nA,比同样尺寸的Schottky-gate HEMT的栅漏电低将近7个数量级。AlGaN/GaN MOS-HEMT的栅压摆幅达到了±20 V。在栅压V_gs=0 V时, MOS-HEMT的饱和电流密度达到了646 mA/mm,相比Schottky-gate HEMT的饱和电流密度(277 mA/mm)提高了133%。栅漏间距为10μm的AlGaN/GaN MOS-HEMT器件在栅压为+3 V时的最大饱和输出电流达到680 mA/mm,特征导通电阻为1.47 mΩ·cm²。Schottky-gate HEMT的开启与关断电流比仅为10⁵,MOS-HEMT的开启与关断电流比超过了10⁹,超出了Schottky-gate HEMT器件4个数量级,原因是栅漏电的降低提高了MOS-HEMT的开启与关断电流比。在V_gs=-14 V时,栅漏间距为10μm的AlGaN/GaN MOS-HEMT的关断击穿电压为640 V,关断泄露电流为27μA/mm。     

具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

介绍了一种具有高阈值电压和大栅压摆幅的常关型槽栅AlGaN/GaN金属氧化物半导体高电子迁移率晶体管。采用原子层淀积(ALD)方法实现Al₂O₃栅介质的沉积。槽栅常关型AlGaN/GaN MOS-HEMT的栅长(L_g)为2 μm,栅宽(W_g)为0.9 mm(0.45 mm×2),栅极和源极(L_gs)之间的距离为5 μm,栅极和漏极(L_gd)之间的距离为10 μm。在栅压为－20 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电仅为0.65 nA。在栅压为+12 V时,槽栅常关型AlGaN/GaN MOS-HEMT的栅漏电为225 nA。器件的栅压摆幅为－20~+12 V。在栅压V_gs=+10 V时,槽栅常关型AlGaN/GaN MOS-HEMT电流和饱和电流密度分别达到了98 mA和108 mA/mm (W_g=0.9 mm), 特征导通电阻为4 mΩ·cm²。槽栅常关型AlGaN/GaN MOS-HEMT的阈值电压为+4.6 V,开启与关断电流比达到了5×10⁸。当V_ds=7 V时,器件的峰值跨导为42 mS/mm (W_g=0.9 mm,V_gs=+10 V)。在V_gs=0 V时,栅漏间距为10 μm的槽栅常关型AlGaN/GaN MOS-HEMT的关断击穿电压为450 V,关断泄露电流为0.025 mA/mm。     

Fabrication and characterization of La-doped HfO2 gate dielectrics by metal-organic chemical vapor deposition

La-doped HfO₂ gate dielectric thin films have been deposited on Si substrates using La(acac)₃ and Hf(acac)₄ (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO₂ films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO₂ films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm² at V_g = 1V + V_fb. MOCVD-derived La-doped HfO₂ is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.     

Effects of heavy-ion irradiation on the electrical properties of rf-sputtered HfO2 thin films for advanced CMOS devices

HfO₂-based metal-oxide semiconductor (MOS) capacitors were irradiated with high-energy ion beam to study the irradiation effects in these films. HfO₂ thin films deposited by radio frequency (rf)-sputtering were irradiated with 80 MeV O⁶⁺ ions. The samples were irradiated and characterized at room temperature. Devices were characterized via 1 MHz capacitance–voltage (C?V) measurements using the midgap method. The irradiation induced dispersion in accumulation and depletion regions with increasing fluence is observed. After irradiation, the midgap voltage shift (Δ V _mg) of?0.61 to?1.92 V, flat band voltage shift (Δ V _fb) of?0.48 to?2.88 V and threshold voltage shift (Δ V _th) of?0.966 to?1.96 V were observed. The change in interface trap charge and oxide trap charge densities after 80 MeV O⁶⁺ ions irradiation with fluences were determined from the midgap to flat band stretch out of C?V curves. The results are reported and explained in terms of changes in microstructure and dielectric properties of the HfO₂ thin films after irradiation.     

Low-temperature deposition of stoichiometric HfO2 on silicon: Analysis and quantification of the HfO2/Si interface from electrical and XPS measurements

An understanding of the exact structural makeup of dielectric interface is crucial for development of novel gate materials. In this paper a study of the HfO₂/Si interface created by the low-temperature deposition ultrathin stoichiometric HfO₂ on Si substrates by reactive sputtering is presented. Analysis, quantification and calculation of layer thickness of an HfO₂/Hf-Si-O_x/SiO₂ gate stack dielectrics have been performed, using X-ray photoelectron spectroscopy (XPS) depth profile method, angle resolved XPS and interface modeling by XPS data processing software. The results obtained were found to be in good agreement with the high frequency capacitance-voltage (C-V) measurements. The results suggest a development of a complex three layer dielectric stack, including hafnium dioxide layer, a narrow interface of hafnium silicate and broad region of oxygen diffusion into silicon wafer. The diffusion of oxygen was found particularly detrimental to the electrical properties of the stack, as this oxygen concentration gradient leads to the formation of suboxides of silicon with a lower permittivity, κ.     

A study on Al2O3 passivation in GaN MOS-HEMT by pulsed stress

This paper studies systematically the drain current collapse in AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors （MOS-HEMTs） by applying pulsed stress to the device. Low-temperature layer of Al2O3 ultrathin film used as both gate dielectric and surface passivation layer was deposited by atomic layer deposition （ALD）. For HEMT, gate turn-on pulses induced large current collapse. However, for MOS-HEMT, no significant current collapse was found in the gate turn-on pulsing mode with different pulse widths, indicating the good passivation effect of ALD Al2O3. A small increase in Id in the drain pulsing mode is due to the relieving of self-heating effect. The comparison of synchronously dynamic pulsed Id - Vds characteristics of HEMT and MOS-HEMT further demonstrated the good passivation effect of ALD Al2O3.     

Effects of packing materials on the sensitivity of RadFET with HfO2 gate dielectric for electron and photon sources

The radiation sensing field effect transistor (RadFET) with SiO₂ gate oxide has been commonly used as a device component or dosimetry system in the radiation applications such as space research, radiotherapy, and high-energy physics experiments. However, alternative gate oxides and more suitable packaging materials are still demanded for these dosimeters. HfO₂ is one of the most attractive gate oxide materials that are currently under investigation by many researchers. In this study, Monte Carlo simulations of the average deposited energy in RadFET dosimetry systems with different package lid materials for point electron and photon sources were performed with the aim of evaluating the effects of package lids on the sensitivity of the RadFET by using HfO₂ as a gate dielectric material. The RadFET geometry was defined in a PENGEOM package and electron–photon transport was simulated by a PENELOPE code. The relatively higher average deposited energies in the sensitive region (HfO₂ layer) for electron energies of 250?keV–20?MeV were obtained from the RadFET with the Al₂O₃ package lid despite of some deviations from the general tendency. For the photon energies of 20–100?keV, the average amount of energy deposited in RadFET with Al₂O₃ package was higher compared with the other capped devices. The average deposited energy in the sensitive region was quite close to each other at 200?keV for both capped and uncapped devices. The difference in the average deposited energy of the RadFET with different package lid materials was not high for photon energies of 200–1200?keV. The increase in the average deposited energy in the HfO₂ layer of the RadFET with Ta package lid was higher compared with the other device configurations above 3?MeV.     

Electrical properties and reliability of HfO2 gate-dielectric MOS capacitors with trichloroethylene surface pretreatment

Trichloroethylene （TCE） pretreatment of Si surface prior to HfO2 deposition is employed to fabricate HfO2 gatedielectric MOS capacitors. Influence of this processing procedure on interlayer growth, HfO2/Si interface properties, gate-oxide leakage and device reliability is investigated. Among the surface pretreatments in NH3, NO, N2O and TCE ambients, the TCE pretreatment gives the least interlayer growths the lowest interface-state density, the smallest gate leakage and the highest reliability. All these improvements should be ascribed to the passivation effects of Cl2 and HC1 on the structural defects in the interlayer and at the interface, and also their gettering effects on the ion contamination in the gate dielectric.     

An AlGaN/GaN HEMT with a reduced surface electric field and an improved breakdown voltage

A reduced surface electric field in an AlGaN/GaN high electron mobility transistor(HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas(2-DEG) channel as an electric field shaping layer.The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions.Compared with the HEMTs with conventional sourceconnected field plates and double field plates,the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge.By optimizing both the length of Mg-doped layer,L m,and the doping concentration,a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure,respectively.In a device with V GS = -5 V,L m = 1.5 μm,a peak Mg doping concentration of 8×10 17cm-3 and a drift region length of 10 μm,the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

Thermal stability of HfO2 nanotube arrays

Thermal stability of highly ordered hafnium oxide (HfO₂) nanotube arrays prepared through an electrochemical anodization method in the presence of ammonium fluoride is investigated in a temperature range of room temperature to 900 °C in flowing argon atmosphere. The formation of the HfO₂ nanotube arrays was monitored by current density transient characteristics during anodization of hafnium metal foil. Morphologies of the as-grown and post-annealed HfO₂ nanotube arrays were analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Although monoclinic HfO₂ is thermally stable up to 2000 K in bulk, the morphology of HfO₂ nanotube arrays degraded at 900 °C. A detailed X-ray photoelectron spectroscopy (XPS) study revealed that the thermal treatment significantly impacted the composition and the chemical environment of the core elements (Hf and O), as well as F content coming from the electrolyte. Possible reasons for the degradation of the nanotube at high temperature were discussed based on XPS study and possible future improvements have also been suggested. Moreover, dielectric measurements were carried out on both the as-grown amorphous film and 500 °C post-annealed crystalline film. This study will help us to understand the temperature impact on the morphology of nanotube arrays, which is important to its further applications at elevated temperatures.