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This paper discusses the influence of deposition conditions on in-situ As doped amorphous silicon emitter films used in NPN RF bipolar transistors. In-situ As doped amorphous and/or polysilicon layers improve electrical performance in BiCMOS devices by reducing the number of process steps and eliminating issues associated with implanted polysilicon on high aspect ratio topographies (plug effect). This study was made using a vertical furnace configuration capable of 150 wafer loads. Because adsorbed AsH3 decomposition species tightly bind to the active surface sites and inhibit the deposition rate, the process recipe is complex. Predictable bipolar parametrics require control of the As diffusion profile within the base region after activation, so a thorough understanding of emitter film growth and dopant incorporation is necessary.
We describe the relationship between process conditions and recipe variants on transistor gain (Hfe), base current (Ib), and emitter resistance (Re). SIMS and in-line sheet resistivity measurements were used to monitor dopant incorporation into the emitter. This data was found to be predictive not only of the Hfe for a population, but also as an indicator of potential “renegade” Hfe behavior.
To investigate the aging effect of a tunneling junction under constant voltage stress, the tunneling resistance and inelastic electron tunneling (IET) spectra were measured. At a low voltage, up to about 0.5 V, the tunneling resistance of junctions increased gradually over time, while above about 0.6V, it decreased gradually. This change was observed independent of voltage polarity. When the applied voltage was positive, the IET spectrum did not change, whereas when it was negative, the IET spectrum changed—the asymmetric peak became symmetric. X-ray photoelectron spectroscopy (XPS) analysis showed that the junction exhibiting an asymmetric peak contained metallic Al at the AlOx/bottom electrode interface, and the junction exhibiting a symmetric peak contained a homogeneous barrier layer. An increase in the tunneling resistance indicates that the amount of metallic Al decreased in the AlO x barrier layer. Transformation from an asymmetric to a symmetric peak indicates that the metallic Al in the AlOx/bottom electrode interface was oxidized, which led to the AlOx layer becoming homogeneous.
Reducing specific contact resistivity of the silicide to silicon interface is advantageous to achieve high planar density and high drive current FET devices. Measuring the differential resistivities at different low voltage bias conditions of four terminal Kelvin test structures with a range of contact sizes has proven particularly effective in characterizing the linearity behavior and specific contact resistivity. This study shows that adding laser activation annealing for an n+ doped silicon contacted by a standard NiPt silicide is found to significantly improve the contact electrical properties. Initial results with only rapid thermal anneal activation show a size dependence of the contact resistivity with non-linear behavior exhibiting maximum resistance at zero bias, and contact resistivities ranging from 4×10-8 Ω-cm2 to 4×10-7 Ω-cm2. Adding laser anneal after the rapid thermal anneal gives ohmic behavior, for contact down to 50nm in size, with a specific contact resistivity of 1×10-8 Ω-cm2. The metal-to-silicide contact resistance was measured separately using a novel test structure and it was confirmed to be negligible. We describe our device structure, our experimental methodology, and the implications of our results for future devices.
We have fabricated two metal/double insulator/metal diodes using a sputtering system and atomic layer deposition. Here, we show metal/double insulator/metal diode applied as a switch element. The diode exhibits good rectifying characteristics at room temperature. We used the electrode material with Pt and insulators were HfO2/ZrO2 and NiO/ZnO each. The devices were fabricated using the lithographic system and top electrode sizes were 30 µm x 30 µ;m. The double insulator diode produces an enhanced nonlinearity by incorporating two adjacent oxides instead of the single oxide layer of the MIM diode. In the double insulator diode the mode of tunneling under positive applied biases can be made different from that under negative applied biases resulting in improved asymmetry.
The precise determination of materials' optical constants in the THz frequency domain is an important new challenge in basic research and is crucial for novel technological applications. Spectroscopic ellipsometry is known as a vital tool for the determination of the materials' dielectric function including its anisotropy. However, ellipsometric measurements at very long wavelengths are difficult due to the lack of reliable sources of sufficient intensity and brilliance. Here we report on our recent advances to use ellipsometry in combination with different electron beam based sources in order to in investigate condensed matter samples in the frequency range from 0.1 to 8 THz. We successfully employ terahertz radiation emitted from two different tunable desktop sources (Smith-Purcell-effect source and a backward wave oscillator) in a polarizer-sample-analyzer ellipsometer scheme. We discuss and present THz range physical material properties due to bound and unbound charge resonances in semiconducting materials. This research will provide important understanding of optical properties for novel materials, inspire new designs, and accelerate development of optical Terahertz devices.
We report the influence of surface treatment, annealing temperature and metal bilayer thickness on the specific contact resistance (ρc) of Au/Ni ohmic contacts to p-GaN and p-AlGaN. Ohmic contact on p-GaN with a hole concentration of 6.5 x 1017 cm-3, shows the lowest ρc of ˜9.2 x 10-6 Ω cm2, when GaN was treated in HCl:H2O (3:1) solution before metal deposition and annealed at 500°C for 10 minutes in 90% N2 and 0% O2 atmosphere. Similar procedure applied on p-AlxGa1-xN (x = 5-7%), with a hole concentration of 2.3 x 1017 cm-3, yields a ρc of 1.8 x 10-4 Ω cm2. An increase is observed in ρc when Mg doping exceeds 4 x 1019 cm-3 in both p-GaN and p-AlGaN. This is attributed to Mg self compensation. This increase is more pronounced in AlGaN which we attribute to the presence of residual native aluminum oxides.
Conductive atomic force microscopy (C–AFM) in ultra high vacuum (UHV) has been used to characterize charge trapping in ultrathin as–deposited oxide films of 2–4 nm (HfO2)x(SiO2)1-x/SiO2 multilayer gate stacks. Pre– and post–stress/breakdown (BD) dielectric degradation is analyzed on a nanoscale. A systematic observation probes stress induced trap generation facilitating physical stack BD. Degradation is considered in terms of the pronounced localized leakage contribution through the high–κ and interlayer SiOx. Simultaneous nanoscale current–voltage (I-V) characteristics and C–AFM imaging illlutrates charge trapping/decay from the native or stress induced traps with intrinsic charge lateral propagation. A post–stress/BD constant voltage imaging shows effects of stress bias polarity on the BD induced topography and trap assisted nano–current variations. Physical attributes of deformed artifacts relate strongly to the polarity of electron injection (gate or substrate) so discriminating the trap generation in high–κ and interlayer SiOx revealing non–homogeneous (dynamic) nature of leakage.
We investigated the amorphous indium gallium zinc oxide (IGZO) based TFT interface properties using synchrotron radiation analysis. Near edge x-ray absorption fine structure shows the presence of N2 molecules between gate dielectric layer and active channel layer. The physical damage enhanced by the sputtering process was the origin of the device degradation evolving molecular state N2.
Since the middle of the 90's, GaN epitaxy techniques have been developed, using either MOCVD or MBE growth methods. A low cost approach is presented aiming at satisfying thermal issues encountered on conventional substrates such as SiC, Sapphire and more recently Silicon. Domain of application are being covered with their associated challenges: RF and High Power applications. Stress engineering is one of the key parameters.
High quality MIM capacitors with improved capacitance density, low leakage currents and linear C(V) behaviour are the object of active research, with potential applications in CMOS, BICMOS and bipolar technologies as filters, analog to digital converters and related radio-frequency operating devices. Several high-k materials (Ta2O5, HfO2, Y2O3, Al2O3-HfTiO, HfON-SiO2) have been put on trial as possible candidates for SiO2 substitution which is required by the aggressive downscaling of electronic devices. Among those, HfO2- based materials seem to offer promising properties, combining a high chemical stability with Si and a high k value. However, HfO2 shows a strong ability to favour charge defects such as oxygen vacancies, which in turn affect the intrinsic properties of devices such as threshold voltage or leakage currents. These oxygen vacancies are actually thought to accumulate in the vicinity of the electrode, thus forming an oxidized interfacial layer and inducing a significant voltage linearity degradation of MIM capacitors.
In this work, it will be shown that this oxide layer thickness can be strongly minimized by using appropriate bottom electrode material. Indeed, high work function materials can efficiently prevent oxygen vacancies charge stocking on their surface. Several MIM devices have been prepared based on HfO2, Al2O3 and SrTiO3 as dielectric materials, and TiN, WSi2.7 and Pt as bottom electrode material. All these devices have been fully characterized in terms of materials properties and electrical behaviour. These results have been analysed and show that a reduced dielectric thickness is preferred to achieve high capacitance density, but is also responsible for voltage linearity degradation. High work function electrode material can help improve this degraded linear behaviour, thanks to the formation of a reduced interfacial oxygen trap layer thickness. Leakage currents seem to be deeply correlated with the morphological state of the dielectric material, an amorphous state being obviously more efficient to prevent current pathways through grain boundaries.
All these results will be presented in detail and discussed with regards to different models proposed in the literature to account for these data.
High electron mobility transistors (HEMTs) with a pseudomorphically strained InAs channel (InAs-PHEMTs) were fabricated, and their high frequency characteristics were estimated by measuring the S-parameters. For a VDS of 1.4 V and VGS of 0.3 V, InAs-PHEMTs showed an excellent intrinsic cut-off frequency (fT, int.) as high as 90 GHz regardless of their longer LG (0.7 μm). Since fT is known to be inversely proportional to LG to the first approximation, fT, int. of our InAs-PHEMTs may reach 630 GHz if their LG is reduced to 0.1 μm.
Moreover, we calculated the InAs-PHEMTs' energy state and potential profile by self-consistently solving the Schrödinger and Poisson equations. In solving the Schrödinger equation, the energy-dependent effective mass was employed to take into account the strong non-parabolicity of InAs conduction-band based on the k·p perturbation theory by E. O. Kane. It was clarified that most electrons are confined to the InAs layer. On the contrary, if the non-parabolicity is not taken into account, electrons will spread over the InGaAs channel layer.
There is continued interest in developing more stable contacts to a variety of GaN-based devices. In this paper we give two examples of devices that show improved thermal stability when boride, nitride or Ir diffusion barriers are employed in Ohmic contact stacks. AlGaN/GaN High Electron Mobility Transistors (HEMTs) were fabricated with Ti/Al/X /Ti/Au source/
drain Ohmic (where X is TiB2, ZrN, TiN, TaN or Ir) contacts and subjected to long-term annealing at 350°C. For GaN layers with an electron concentration of ∼3×1017 cm-3, the minimum specific contact resistance achieved is 6×10-5 Ω cm2 for Ti/Al/TiN/Ti/Au after annealing at 800°C. The specific contact resistance was found to strongly depend on the doping level, suggesting that tunneling is the dominant mechanism of current flow. By comparison with companion devices with conventional Ti/Al/Ni/Au Ohmic contacts, the HEMTs with boride-based Ohmic metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350°C. The gate current for standard HEMTs increases during aging and the standard Ohmic contacts eventually fail by shorting to the gate contact. Similarly, InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni/Au/TiB2/Ti/Au or Ni/Au/Ir/Au p-Ohmic contacts. Both of these contacts showed superior long-term thermal stability compared to LEDs with conventional Ni/Au contacts.
Comparative analysis of GaAs semiconductor radiation detectors and silicon pixel ones with internal amplification elaborated for detection of nuclear radiation is carried out. Electrophysical and spectral characteristics are compared.
Both the detector types have high sensitivity to α, β and γ radiation and can be applied in space and accelerator experiments for energy determination of elementary particles as well as in astrophysics, transmission and reflecting electron microscopy, medicine, biology and so on.
It is shown that solution-grown ZnO nanostructures exhibit enhanced radiation hardness against neutron irradiation as compared to bulk material. The decrease of the cathodoluminescence intensity after irradiation at a neutron dose of 6 × 1016 cm−2 in ZnO nanostructure is nearly identical to that induced by a dose of 1.5 × 1014 cm−2 in bulk material. The damage introduced by irradiation is shown to change the nature of electronic transitions responsible for luminescence. The change of excitonic luminescence to the luminescence related to the tailing of the density of states caused by potential fluctuations occurs at an irradiation dose around 6×1016 cm−2 and 5×1014 cm−2 in nanostructured and bulk materials, respectively.
Hall measurements before and after annealing determined the effect of dose on resistance, mobility, and carrier concentration. Annealing decreased the sheet resistance, increased the mobility, and increased carrier concentration for all doses. While the concentration of carriers in the control sample increased 200-fold after annealing, the increase was ∼1000-fold for the irradiated samples. Annealed irradiated samples showed a maximum carrier concentration increase of about 60x over the unirradiated sample. Interestingly, neutron irradiation increased the mobility even in the un-annealed samples.
a-IGZO TFT is a promising candidate device for an alternative to poly-Si TFTs or a-Si TFTs, because they provide better uniformity in terms of their important device parameters, including the threshold voltage and mobility due to their amorphous phase, and a high mobility (>10 cm2/Vs) is attainable with these devices even in the amorphous phase. Recently, a-IGZO TFTs have been extensively studied by various groups. However, there is little report on interface and bulk effect on device performances and reliability as separately. For investigating the interface and bulk effect, we fabricated two a-IGZO thin film transistors with different channel deposition conditions, RF and DC magnetron sputtering. Specific conditions of RF and DC sputtering are described as follows; magnetron power density of 1.4 W/cm2/2.0 W/cm2 in Ar/O2 gas ratio of (65/35)/(72/28), and the entire gas pressure was 5.0 mTorr and 3.4 mTorr, respectively.In order to characterize the channel quality, C-V curve was measured with various frequencies of (10KHz˜1MHz). RF sputtered channel has higher frequency dependency compared to DC sputtered channel. It means that RF sputtered channel has higher bulk traps in channel compared to DC sputtered channel.
Device performance was characterized through the ID-VG measurement. Electrical parameters of RF and DC sputtered devices are VT=3.5/2.7V, on-off ratio=105/08, SS=2/0.4 V/decade, and uFE= 5/11 cm2/V-s, respectively. It is thus clear that the device performance of DC sputtered device is more superior to RF sputtered device. Therefore, it can be said that the poor device performance of RF device is ascribed to insufficient channel quality, as mentioned in C-V curve.
For reliability study, we measured PBTI and ID-VG hysteresis with normalized gate stress bias and high temperature hot chuck system. Through the unchanged field effect mobility during the stress and relaxation time, and nearly recovered VT and subthreshold slope (SS) after long relaxation time, we were able to know that pre-existed trap was main factor of reliability degradation. Moreover, SS degradation during stress time is more severe in RF device than DC device. It is also proving that RF channel characteristic is worse than DC channel. In high temperature, leakage current increments of RF device were more severe than DC device. This also indicates that bulk traps of RF device in channel region are larger than that of DC device. VT shift of DC sputtered device for PBT stress and hysteresis was higher than that of RF sputtered device. As well known, PBTI is closely related to insulator bulk traps, which shows that channel deposition conditions affect insulator trap characteristics. In summary, device performance of a-IGZO deposited by DC sputtering is better than RF sputtering, which is because DC sputtering improves channel quality of a-IGZO. However, VT shift of DC sputtered device are worse than RF sputtering, which may be related with high magnetron power density.
InGaN/GaN MQWs are grown on c-plane sapphire substrates using a low pressure metal organic vapor phase epitaxy (MOVPE) system. Trimethylgallium (TMGa), Triethylgallium (TEGa), Trimethylindium (TMIn) and ammonia were used as precursors for Ga, In and N, respectively and the growths were carried out at low temperature. Structural properties of grown MQWs are characterized using atomic force microscopy (AFM), and scanning electron microscope (SEM) and x-ray diffraction technique (XRD) is used to calculate the Indium incorporation in these MQWs. Surface morphologies over large areas of InGaN/GaN MQWs are observed using the tapping mode AFM; results indicate the surface roughness depends on the barrier thickness. Density of V- defects, effect of barrier width on the surface morphology and also on V-defect density will be presented and discussed.
In this work we explore both the initial nucleation and the stoichiometry of rutile-TiO2(001) grown on wurtzite GaN(0001) by radio-frequency O2-plasma molecular beam epitaxy. Two studies are performed; in the first, the dependence of the growth on stoichiometry (Ti-rich and O-rich) is observed using reflection high energy electron diffraction and high resolution transmission electron microscopy. In the second study we examine the effect of different initial nucleation surfaces (i.e. Ga-terminated and excess Ga-terminated) and compare the interfaces and bulk crystallinity of the TiO2(001) films grown on top of these surfaces. High-resolution transmission electron microscopy and x-ray diffraction measurements show a better interface for TiO2(001)/Ga-terminated - GaN(0001) as compared to the TiO2(001)/excess Ga-terminated- GaN(0001).
Orientation patterned (OP)-GaAs crystals show promise for use in tunable coherent light sources in the infrared (IR) and terahertz (THz). These structures consist of an alternating array of /[00-1] oriented domains grown by hydride vapor phase epitaxy (HVPE). Material characteristics concerning the propagation losses, the crystal dimensions, and the grating size must be taken into account to implement optical devices for specific wavelength ranges and operating modes (CW or pulsed). The analysis of the main factors contributing to optical loss in the OP crystals is a crucial step toward their use in many promising applications. We present a cathodoluminescence study, where the main defects and their distribution over the OP-GaAs crystals are revealed, with special emphasis paid to the properties of the domain walls.
Thin films of boron carbon nitride (BCN) and boron carbide (BC) were synthesized by plasma enhanced chemical vapor deposition (PECVD) using two different reactant chemistries: (i) N,N’,N” – trimethylborazine (TMB); (ii) dilute diborane (5% in Ar) and hydrocarbon as precursor materials. Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Nano-Indentor, Flexus stress instrument and x-ray photoelectron spectroscopy were used to study the deposited films. The BC films are much more stable than BCN films under high humidity (100%) environment. Both BCN and BC films are very stable under atmospheric conditions. A high compressive stress of -4.2 GPA was achieved by conventional PECVD, which show promising applications in high performance ultra large-scale integrated circuit (ULSI) devices.
This paper presents electrical transfer (Id-Vg) and output (Id-Vds) characteristics of a GeOx-cladded-Ge quantum dot (QD) gate Si MOSFET devices. In QD gate FETs, the manifestation of an intermediate state ‘i” makes it a 3-state device. The intermediate state originates due to compensation of increment in the gate voltage by a similar increase in the threshold voltage, which occurs via charge neutralization in the QD gate due to transfer of charge from the inversion layer to either first or second of the two QD layers.