STI-to-gate distance effects on flicker noise characteristics in 0.13 μm CMOS

The geometry effect on the flicker noise characteristics and the variations in 0.13 μm CMOS transistors were studied. By symmetrically extending the distance between the shallow-trench-isolation (STI) to the gate, both NMOS and PMOS presented obvious improvement on the noise characteristics. As the distance increased from 0.6 μm to 10 μm, the average noise level reduced by more than one order of magnitude (NMOS) and the standard deviations σ_dB improved from 5.95 dB to 1.79 dB for NMOS and from 3.93 dB to 2.17 dB for PMOS, respectively. To further identify the noise mechanism, the devices with asymmetrical STI-to-gate distances were also investigated. It was found that the distance in the source side (SA) has a much higher impact on the observed noise characteristics. The results suggested that the noise characteristics were dominated by the STI stress induced traps for both NMOS and PMOS studied here. In addition, the carrier number fluctuation model with the correlated mobility scattering could be more suitable to describe the noise characteristics in these devices.     

Static and low frequency noise characterization of surface- and buried-mode 0.1 μm P and N MOSFETs

This work presents the low frequency noise and the electric performances in terms of output/transfer characteristics, threshold voltage, and short channel effect in both NMOS and PMOS transistors for 0.1 μm technologies. For the last one there are two architectures based either on a surface mode of operation (surface channel) or on a buried one (buried channel) featuring either a P+ or a N+ polysilicon gate material. The impact of the channel length on the noise characteristics as well as on the output/transfer characteristics is studied. We find that the 1/f noise can be interpreted in terms of carrier number fluctuations for both N and P channel MOSFETs for surface and buried mode of operation. The oxide trap density Nt is therefore evaluated, demonstrating an overall good oxide quality.     

Static and low frequency noise characterization of surface- and buried-mode 0.1 μm P and N MOSFETs

This work presents the low frequency noise and the electric performances in terms of output/transfer characteristics, threshold voltage, and short channel effect in both NMOS and PMOS transistors for 0.1 μm technologies. For the last one there are two architectures based either on a surface mode of operation (surface channel) or on a buried one (buried channel) featuring either a P+ or a N+ polysilicon gate material. The impact of the channel length on the noise characteristics as well as on the output/transfer characteristics is studied. We find that the 1/f noise can be interpreted in terms of carrier number fluctuations for both N and P channel MOSFETs for surface and buried mode of operation. The oxide trap density Nt is therefore evaluated, demonstrating an overall good oxide quality.     

Degenerate cadmium oxide films for electronic devices

Highly conducting and transparent cadmium oxide films have been deposited on Corning 7059 glass substrates by ion-beam sputtering and by spray pyrolysis. The electrical and optical properties of CdO films prepared by the two techniques are similar. Typical films of 0.5 μm thickness have electrical resistivities of (2–5) × 10^-3 ohm-cm, carrier concentrations of approximately 10²⁰ cm^-3, and an optical transmission of higher than 70% in the wavelength range of 600–900 nm. An optical bandgap of 2.4–2.42 eV was deduced from the optical transmission data.     

Electrical properties of molecular beam epitaxial GaAs grown at 300–450°C

We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300–450°C. Layers grown from 350–450°C are semi-insulating (resistivity greater than 10⁷ Ω-cm), as grown, because of an As_Ga-related donor (not EL2) at E_C-0.65 eV. The donor concentrations are about 2×10¹⁸ cm⁻³ and 2×10¹⁷ cm⁻³ at growth temperatures of 300 and 400°C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities (∼5000 cm²/V s) along with the high resistivities make this material potentially useful for certain device applications.     

High-energy proton irradiation effects on AlGaN/GaN high-electron mobility transistors

AlGaN/GaN high-electron mobility transistors (HEMTs) show decreases in extrinsic transconductance, drain-source current threshold voltage, and gate current as a result of irradiation with 40 MeV protons at doses equivalent to decades in low-earth orbit. The data are consistent with the protons creating deep electron traps that increase the HEMT channel resistance. Postirradiation annealing at 300°C was able to restore ∼70% of the initial g_m and I_DS values in HEMTs receiving proton doses of 5×10¹⁰ cm⁻².     

The effect of annealing temperature on the carrier concentration OF Hg0.6Cd0.4Te

The carrier concentration dependence of Hg_0.6Cd_0.4Te on annealing temperature for the Hg and Te saturation condi-tions is presented in this paper. At low annealing tempera-tures, T_A < 350‡ C, residual donor impurities apparently limit the carrier concentration. In contrast, at higher annealing temperatures, 350‡ C < T < 700‡ C, the stoichio-metric acceptor density is increased such that the residual donors are compensated and the material is converted to p-type with an acceptor density as large as 10¹⁷ cm⁻³ . An empirical expression describing this dependence of the acceptors on annealing temperature is given for both the Hg and Te saturation condition: P (Hg saturation) = 1.46 × 10²² exp (−0.84/kT_A), P (Te saturation) = 1.90 × 10¹⁸ exp (−0.15/kT_A). Supported in part by Air Force Materials Laboratory, WPAFB, Ohio under Contract AF61533-C-74-5041.     

Growth and electronic properties of ZnO epilayers by plasma-assisted molecular beam epitaxy

ZnO thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy (MBE). The crystalline properties of the layers as measured by x-ray diffraction were found to improve with lower growth temperatures, where the full-width at half-maximum (FWHM) of the x-ray rocking curves was shown to be in the range of 100 to 1,100 arcsec. The electronic properties were found to improve for higher growth temperatures, with n-type carrier concentration and electron mobility in the range of 1×10¹⁷ −5×10¹⁸ cm⁻³ and 80–36 cm²/Vs, respectively. Photoluminescence (PL) measurements indicated that growth at higher temperatures provided superior band edge radiative emission, while growth at lower temperatures resulted in significant deep level radiative emission centered at 2.35 eV. Photoconductive decay measurements exhibit a slow decay indicating the presence of hole traps, where Zn vacancies are believed to be the source of both the slow decay and the deep level emission observed in PL spectra.     

Dependence of electrical properties of polycrystalline cvd si films on grain size and impurity doping concentrationa,b

The electrical properties of sets of simultaneously grown p-type polycrystalline Si films, deposited by SiH₄ pyrolysis on polycrystalline high-purity alumina substrates and B-doped during growth, were determined by Hall-effect measurements in the temperature range 77-420K as functions both of impurity doping concentration N (~10^l5 to ~10²⁰cm⁻³) and average grain size (≈1 to ≈125μm) in the film. Room temperature data showed rapidly increasing resistivities and rapidly decreasing free-carrier concentrations for doping below a critical concentration N_m and distinct mobility minima at that concentration, with the value of N_m being larger the smaller the average grain size. Measurements as a function of sample temperature showed the intergrain barrier height E_b, decreasing from a maximum value of ~0.4eV at the critical concentration to very small values (~0.01eV) for concentrations above 10¹⁹cm⁻³, with a functional dependence close to E_b ∝l/N^1/2 and E_b for any given concentration being larger the smaller the average grain size. Results are interpreted in terms of the grain-boundary trapping model. Trapped carrier densities in the grain boundaries were calculated to range from ~5×l0¹¹cm⁻² at N≈N_m to ~5×l0¹²cm⁻² for N>10¹⁹cm⁻³, the density being higher the smaller the grain size, and evidence was found for an energy distribution of traps in the Si bandgap, rather than a fixed density at a single discrete energy level. The observed relationship between N_m and average grain size nearly coincides with that of the model for films with ~lμm grain size but sharply departs from it for larger grain sizes, indicating probable applicability of the model for grain sizes up to that range. ^aThis work was supported by the U.S. Department of Energythrough its San Francisco Operations Office under Contract DE-AC03-79ET23045 and monitored by the Solar Energy Research Institute, Golden, CO. bThese results were first described at the 22nd Electronic Materials Conference, Ithaca, NY, June 21–27, 1980, Paper No. M4.     

Simultaneous formation of p- and n-type ohmic contacts to 4H-SiC using the ternary Ni/Ti/Al system

Fabrication procedures for silicon carbide power metal oxide semiconductor field effect transistors (MOSFETs) can be improved through simultaneous formation (i.e., same contact materials and one step annealing) of ohmic contacts on both the p-well and n-source regions. We have succeeded with the simultaneous formation of the ohmic contacts for p- and n-type SiC semiconductors by examining ternary Ni/Ti/Al materials with various compositions, where a slash symbol “/” indicates the deposition sequence starting with Ni. The Ni(20 nm)/Ti(50 nm)/Al(50 nm) combination provided specific contact resistances of 2 × 10⁻³ Ω-cm² and 2 × 10⁻⁴ Ω-cm² for p- and n-type SiC, respectively, after annealing at 800°C for 30 min, where the doping level of Al in the SiC substrate was 4.5 × 10¹⁸ cm⁻³ and the level of N was 1.0 × 10¹⁹ cm⁻³.     

Comparison of MOS capacitors on n- and p-type GaN

The electrical characteristics of both n- and p-type GaN metal-oxide semiconductor (MOS) capacitors utilizing plasma-enhanced CVD-SiO₂ as the gate dielectric were measured. Both capacitance and conductance techniques were used to obtain the MOS properties (such as interface state density). Devices annealed at 1000°C/30 min. in N₂ yielded an interface state density of 3.8×10¹⁰ cm⁻² eV⁻¹ at 0.19 eV from the conduction band edge, and it decreased to 1.1×10¹⁰ cm⁻² eV⁻¹ deeper into the band gap. A total fixed oxide charge density of 8×10¹² q cm⁻² near the valence band was estimated. Unlike the symmetric interface state density distribution in Si, an asymmetric interface state density distribution with lower density near the conduction band and higher density near the valence band was determined.     

Application of combinatorial methodologies for work function engineering of metal gate/high-κ advanced gate stacks

This paper uses combinatorial methodologies to investigate the effect of TaN-AlN metal gate electrode composition on the work function, for (TaN-AlN)/Hf-Si-O/SiO₂/Si capacitors. We demonstrate the efficacy of the combinatorial technique by plotting work function for more than thirty Ta_1-xAl_xN_y compositions, with x varying from 0.05 to 0.50. The work function is shown to continuously decrease, from about 4.9 to about 4.7 eV, over this range. Over the same range, oxide fixed charge is seen to go from about -2.5 × 10¹² cm⁻³ to about zero. The work functions reported here are about 0.1 eV higher than in a previous study, but are still about 0.2 eV smaller than required for PMOS device applications.     

Effects of Illumination on Ar<Superscript>+</Superscript>-Implanted <Emphasis Type="Italic">n</Emphasis>-Type 6H-SiC Epitaxial Layers

Argon ions were implanted into n-type 6H-SiC epitaxial layers at 600°C. Postimplantation annealing was carried out at 1,600°C for 5 min in an Ar ambient. Four implantation-induced defect levels were observed at E_C-0.28 eV, E_C-0.34 eV, E_C-0.46 eV, and E_C-0.62 eV by deep level transient spectroscopy. The defect center at E_C-0.28 eV is correlated with ED₁/ED₂ and with ID₅. The defect at E_C-0.46 eV with a capture cross section of 7.8 × 10⁻¹⁶ cm² is correlated with E1/E2, while the defect at E_C-0.62 eV with a capture cross section of 2.6 × 10⁻¹⁴ cm² is correlated with Z1/Z2. Photo deep level transient spectroscopy was also used to study these defects. Upon illumination, the amplitudes of the deep level transient spectroscopy (DLTS) peaks increased considerably. Two emission components of Z1/Z2 were revealed: one fast and the other slow. The fast component could only be observed with a narrow rate window. In addition, a new defect was observed on the low-temperature side of the defect at E_C-0.28 eV when the sample was illuminated. [rl](Received ...; accepted ...)     

Variable area MWIR diodes on HgCdTe/Si grown by molecular beam epitaxy

Molecular beam epitaxy technique has been used to grow double layer heterostructure mercury cadmium telluride materials on silicon substrates for infrared detection in the mid-wavelength infrared transmission band. Test structures containing square diodes with variable areas from 5.76 × 10⁻⁶ cm² to 2.5×10⁻³ cm² are fabricated on them. The p on n planar architecture is achieved by selective arsenic ion implantation. The absorber layer characteristics for the samples studied here include a full width at half maximum of 100–120 arcsec from x-ray rocking curve, the electron concentration of 1−2 × 10¹⁵ cm⁻³ and mobility 3−5 × 10⁴ cm²/V-s, respectively at 80 K from Hall measurements. The minority carrier lifetime measured by photoconductive decay measurements at 80 K varied from 1 to 1.2 μsec. A modified general model for the variable area I–V analysis is presented. The dark current-voltage measurements were carried out at 80 K and an analysis of the dependence of zero-bias impedance on the perimeter/area ratio based on bulk, surface generation-recombination, and lateral currents are presented. The results indicate state-of-the art performance of the diodes in the midwavelength infrared region.     

Zinc-doped CdS nanoparticles synthesized by microwave-assisted deposition

Cd_1-xZn_xS nanoparticles were grown on pre-cleaned glass substrates using microwave-assisted chemical bath deposition technique. Nanoparticles obtained by this method were smooth, uniform, good adherent, brownish yellow in color where the brightness of the yellow color nature decreases with increasing Zn²⁺ content. The elemental composition analysis confirmed that the nanoparticles comprise of Cd²⁺, Zn²⁺and S^2-. Scanning electron microscope images confirmed the surface uniformity of the Cd_1-xZn_xS nanoparticles devoid of any void, pinhole or cracks and covered the substrate well. The particle size also decreases with increasing Zn ion content. X-ray diffraction (XRD) indicates the hexagonal structure (002) without phase transition. The grain size decreases from 36.45 to 9.60 nm, dislocation density increases from 0.000745 to 0.01085 Line²/m² and lattice parameter decreased from 6.868 to 6.155 nm with increasing Zn²⁺ content. The best transmittance of about 95% was achieved for x=1.0. The nanoparticles showed reduction in the absorbance as Zn ion content increased. Four point probe revealed that the electrical resistivity increased from 1.51×10¹⁰ to 6.67×10¹⁰ Ω ·cm while electrical conductivity decreases from 6.62×10^-11 to 1.49×10^-11 (Ω ·cm)^-1 with increasing Zn²⁺ content. The other electrical properties such as sheet resistance increased from 1.52×10⁸ to 1.58×10⁸Ω, charge carrier mobility decreased from 0.777 to 0.0105 cm²/(V·s) and charge carrier density increased from 1.06×10¹² to 3.95×10¹² cm^-3.     

Defect chemistry and intrinsic carrier concentration for Hg1−x Cdx Te(s) for x = 0.20, 0.40, and 1.0

The theoretical equations governing the crystal-vapor equilibrium for Hg_1−x Cd_x Te(s) are summarized for a model with doubly-ionized native defects and applied to the data for x = 0.20, 0.40, and 1. The basic equations (Eq. (1) or (19)) are shown to contain those used elsewhere as special cases. Allowing the intrinsic carrier concentration, n₁, to vary, but under constraints, to obtain an optimum fit and assuming a non-degenerate semiconductor, the hole con-centration-mercury pressure isotherms can be fitted satis-factorily and better than before with standard deviations between 22 and 24% for x = 0.20 and 0.40. A number of sets of model parameters give these fits, some of which give values as large as 10/cm at 500δC for the square root of the Schottky constant for ionized vacancies. In agreement with experiment, each of these parameter sets for x = 0.20 and 0.40 predicts a negligible dependence of the 77 and 192 K Hall mobilities upon equilibration temperature and predicts that metal saturation between 250 and 300δC with foreign donors in the 10¹⁵/cm³ range will result in elec-tron concentrations in the same range and dependent on saturation temperature to less than 26%. The enthalpy to create a “Hg-vacancy” and two holes is an invariant of the fits and is 2.00 ± 0.04 eV for x = 0.40 and 1.94 ± 0.02 eV for x = 0.20. Then n_i is calculated independently assuming a parabolic valence band and a Kane conduction band. With an exact density of states for the latter obtained here, the momentum matrix element, P = 8.5 × 10₋₈ eV-cm, the spin-orbit splitting, Δ = 1 eV, and E (x, T) from Hansen et al., the experimental values below 300 K for 0 ≤x = 0.3 and at high temperature for x = 1 are fitted well with m _h ^∗ /m = 0.70. With these independently calculated values for n_i the electron concentration-cadmium pressure isotherms for CdTe can be fitted to about 7% for either of two incon-sistent data sets assuming 2 × 10¹⁶ /cm³ foreign donors. However data for x = 0.40 can be fitted to only 42% and that for x = 0.20, which is degenerate, to only 28%.     

Interface studies of the MOS-structure by transfer-admittance measurements

The transfer-admittance of n- and p-channel MOS transistors has been measured under the condition of a uniform channel. These MOS transistors all showed a measurable “slow interface state drift” <0·1–0·2 V. The transfer-susceptance has been found to show a significant peak value in moderate inversion. Over the entire moderate and strong inversion region the transfer-susceptance remains constant as a function of the measurement frequency ω between 1·6 Hz and 2 × 10⁴ Hz, while the transfer-conductance varies almost like ln ω. Furthermore the transfer-susceptance shows a linear relationship with the variation of the transfer-conductance per frequency decade. The paper shows that these phenomena can be well explained by assuming a tunneling of channel charge carriers into electron states in the oxide. Also the temperature behaviour of the transfer-admittance does not seem to be in conflict with this tunnel model. More than the CV measuring method the measurement of the transfer-admittance allows an investigation of the interaction between mobile inversion layer charge carriers, and interface states in the condition of moderate inversion (5 × 10¹⁰-5 × 10¹¹ electrons cm^?2). The measuring method might therefore find application in the investigation of charge trapping in CCD devices. As a pertinent result the density of oxide states having time constants between 6 × 10^?1 sec and 1·6 × 10^?5 sec appears to increase to values of about 10¹¹ per cm²V as the interface state energy approaches the conduction and valence band edge energies within a distance of ? 70 meV.     

Tailoring the Structural and Optoelectronic Properties of Al-Doped Nanocrystalline ZnO Thin Films

This paper describes the effect of Al doping (0 at.% to 6 at.%) on the structural and optoelectronic properties of nanocrystalline ZnO thin films deposited by thermal evaporation. X-ray diffraction patterns confirm that an increase in Al concentration (from 0% to 6%) in ZnO lowers the crystallinity of the films and reduces grain size. Al doping is also found to influence the optical properties of the ZnO thin films. Visible transmittance above 85% was obtained by increasing the Al doping to 6%. The optical bandgap was found to vary from 3.20 eV to 3.97 eV with changing Al content from 0% to 6%, which is in accordance with the Burstein–Moss shift. The mobility of ZnO thin films can be varied from 5.60 cm²/Vs to 24.25 cm²/Vs, the carrier concentration from 5.93 × 10¹⁸/cm³ to 9.11 × 10²⁰/cm³, and the resistivity from 4.62 × 10⁻⁴ Ω cm to 4.34 × 10⁻² Ω cm, depending on the Al doping concentration (0% to 6%). This study suggests that ZnO:Al films can be tailor-made to meet the requirements for various optoelectronic applications such as flexible photocells or ultraviolet (UV) photodetectors covering a wide range of short wavelengths.     

Minority carrier lifetime and noise in abrupt molecular-beam epitaxy-grown HgCdTe heterostructures

The steady-state lifetime of photogenerated minority carriers has been investigated in heterostructure HgCdTe devices fabricated on molecular-beam epitaxy (MBE) grown material. A wider bandgap capping layer (Hg_(1−x)Cd_(x)Te, x = 0.44) was grown on a narrower bandgap absorbing layer (Hg_(1−x)Cd_(x)Te, x = 0.32, λ_co,80K = 4.57 μm) material in an uninterrupted MBE growth to create an abrupt heterointerface. Steady-state lifetime as a function of temperature over the range 80–300 K was extracted from photoconductive responsivity at an optical wavelength corresponding to the peak responsivity at that temperature. At 80 K, the photoconductors exhibit a specific detectivity of 4.5 × 10¹¹ cm Hz^−1/2W⁻¹ (chopping frequency of 1 kHz). For each measurement temperature, the steady-state excess carrier lifetime determined experimentally was compared to the theoretical bulk lifetime for material with x = 0.32 and effective n-type doping density of 3.7 × 10¹⁴ cm⁻³. Theoretical calculations of the Auger-1 lifetime based on expressions developed by Pratt et al. were not able to account for the reduction in lifetime observed at temperatures above 180 K. Two approaches have been attempted to resolve this discrepancy: A semiempirical expression for Auger lifetime attributed to Meyer et al. was used to fit to the data, with the Auger coefficient γ as a fitting parameter. However, the resulting Auger coefficient found in this work is more than an order of magnitude higher than that reported previously. Alternatively, the reduction in effective lifetime above 180 K may be understood as a “loss” of carriers from the narrow bandgap absorbing layer that are promoted across the potential barrier in the conduction band into a low lifetime, wider bandgap capping layer. The reduction in lifetime as a function of inverse temperature for temperatures above 180 K may be fitted by a “cap lifetime” that has an activation energy equal to the change in bandgap across the heterostucture and scaled by a fitting constant.     

Characteristics of surface states at the insulator-semiconductor interface in the thin-film electroluminescent structures based on ZnS:Mn

Distributions of the density of occupied surface electron states at the cathode interface between the insulator and phosphor in thin-film electroluminescent emitters are simulated in relation to the energy on the basis of experimental data. The dependences of the above distributions on the conditions of excitation of emitters are obtained. It is shown that these distributions shift to deeper levels of surface states as the frequency of excitation voltage is decreased and the pause between two neighboring switched-on states of emitters is increased, which corresponds to the cascade mechanism of relaxation of electrons captured by surface states. The coefficient of cascade capture of electrons prior to relaxation ((4−5) × 10⁻¹² cm²/s), instantaneous lifetime of electrons prior to relaxation (0.2–0.25 s), cross section for capture of electrons to deeper levels of surface states (in excess or on the order of (6.7−8.3) × 10⁻²¹ cm²), largest values of the densities of occupied surface states at the cathode boundary from which electron tunnel (∼2.5 × 10¹³ cm⁻²), and energy density of above-specified surface states (7 × 1014 cm⁻² eV⁻¹) have been determined. The values of the quasi-equilibrium Fermi level at the surface in the course of the activity of electroluminescent emitters varies in the range from 0.9 to 1.35 eV, depending on conditions of excitation.