Estimation for the capture cross-sections of surface state on p-Si surface by photovoltaic method

A new method which can nondestructively measure the surface-state density (SSD) D_s and estimate the capture cross-sections (CCS) of surface state σ⁰_n and σ⁻_p on surface of p-type semiconductor crystals is proposed. This method is based on the photovoltage measurements at various temperatures. The photovoltage experiment was carried out with a (1 1 1) p-type Si single crystal (N_A=4.8×10¹⁴ cm ⁻³). Owing to that the surface barrier height φ_BP=0.6421 V and the surface-recombination velocity s_n=9.6×10³ cm s⁻¹ of this sample can be determined, the SSD D_s=1.2×10¹¹ cm⁻² eV⁻¹ can therefore be obtained, furthermore CCS σ⁰_n≈5×10⁻¹⁴ cm² and σ⁻_p≈2×10⁻¹⁰ cm² can also be estimated. These results are consistent with that of related reports obtained by other methods.     

Optoelectronic properties of Zn0.52Se0.48/Si Schottky diodes

Zn_0.52Se_0.48/Si Schottky diodes are fabricated by depositing zinc selenide (Zn_0.52Se_0.48) thin films onto Si(1 0 0) substrates by vacuum evaporation technique. Rutherford backscattering spectrometry (RBS) analysis shows that the deposited films are nearly stoichiometric in nature. X-ray diffractogram of the films reveals the preferential orientation of the films along (1 1 1) direction. Structural parameters such as crystallite size (D), dislocation density (δ), strain (ε), and the lattice parameter are calculated as 29.13 nm, 1.187 × 10⁻¹⁵ lin/m², 1.354 × 10⁻³ lin⁻² m⁻⁴ and 5.676 × 10⁻¹⁰ m respectively. From the I–V measurements on the Zn_0.52Se_0.48/p-Si Schottky diodes, ideality and diode rectification factors are evaluated, as 1.749 (305 K) and 1.04 × 10⁴ (305 K) respectively. The built-in potential, effective carrier concentration (N_A) and barrier height were also evaluated from C–V measurement, which are found to be 1.02 V, 5.907 × 10¹⁵ cm⁻³ and 1.359 eV respectively.     

Avalanche breakdown voltage of GaAs hyperabrupt junctions

The avalanche breakdown voltage of a GaAs hyperabrupt junction diode is calculated by using unequal ionization rates for electrons and holes, and shown graphically as a function of the parameters which characterize the impurity profile of the diode. The breakdown voltage decreases abruptly at the critical point of the characteristic length L_c which varies in accordance with the impurity concentration N₀ at X = 0. For example, the critical length L_c is 7.7 × 10⁻⁶ cm and 3.3 × 10⁻⁵ cm for N₀ = 1 × 10¹⁸ cm⁻³ and 1 × 10¹⁷ cm⁻³, respectively. The breakdown voltage of a diode with extremely short or long characteristic length can be estimated from the results for corresponding abrupt junctions. The experimental results agree well with the calculated ones.     

Schottky barrier height of a new ohmic contact NiSi2 to n-type 6H-SiC

We present a new ohmic contact material NiSi₂ to n-type 6H-SiC with a low specific contact resistance. NiSi₂ films are prepared by annealing the Ni and Si films separately deposited on (0 0 0 1)-oriented 6H-SiC substrates with carrier concentrations (n) ranging from 5.8×10¹⁶ to 2.5×10¹⁹ cm⁻³. The deposited films are annealed at 900 °C for 10 min in a flow of Ar gas containing 5 vol.% H₂ gas. The specific contact resistance of NiSi₂ contact exponentially decreases with increasing carrier concentrations of substrates. NiSi₂ contacts formed on the substrates with n=2.5×10¹⁹ cm⁻³ show a relatively low specific contact resistance with 3.6×10⁻⁶ Ω cm². Schottky barrier height of NiSi₂ to n-type 6H-SiC is estimated to be 0.40±0.02 eV using a theoretical relationship for the carrier concentration dependence of the specific contact resistance.     

Thin oxide grown on heavily channel-implanted substrate by using a low temperature wafer loading and N2 pre-annealing process

In this paper, we present high integrity thin oxides grown on the channel implanted substrate (3 × 10¹⁷ cm⁻³) and heavily doped substrate (1 × 10²⁰ cm⁻³) by using a low-temperature wafer loading and N₂ pre-annealing process. The presented thin oxide grown on the channel implanted substrate exhibits a very low interface state density (1 × 10¹⁰ cm⁻² eV⁻¹) and a very high intrinsic dielectric breakdown field (15 MV/cm). It also shows a lower charge trapping rate and interface state generation rate than the conventional thermal oxide. For the thin oxide grown on the heavily-doped substrate by using the proposed recipe, the implantation-induced damage close to the silicon surface can be almost annealed out. The presented heavily-doped oxide shows much better dielectric characteristics, such as the dielectric breakdown field and the charge-to-breakdown, as compared to the conventional heavily-doped oxide.     

Intersubband lifetimes in Si/SiGe quantum wells

In the present work we report the first measurement of intersubband lifetimes in Si/Si_1−xGe_x quantum well samples. We have determined T₁ by a time resolved pump and probe experiment using the far infrared picosecond free electron laser source FELIX at Rijnhuizen, the Netherlands. In a sample with a well width of 50 Å and a sheet density of 2.1 × 10¹² cm⁻² we find a lifetime of 30 ps while 20 ps is observed for a density of 1.1 × 10¹² cm⁻² and a well width of 75 Å. We discuss acoustic phonon, as well as optical phonon intersubband scattering as possible limiting processes for the observed lifetimes in Si/SiGe and GaAs/AlGaAs quantum wells.     

Interface characteristics of Ge3N4-(n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge₃N₄ dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C-V-f and G-V-f measurements, density of interface states has been obtained as (4–6)×10¹¹ cm⁻² eV⁻¹ at the semiconductor mid-gap. Some inversion charge buildup was seen in the C-V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10¹⁸−10¹⁹ cm⁻³ in the dielectric film, with their energy level at 0.59 eV.     

Metal-germanium Schottky barriers

A systematic study has been made of the electrical characteristics of Schottky barriers fabricated by evaporating various metal films on n-type chemically cleaned germanium substrates. The diodes, with the exception of Al---Ge contacts, exhibit near-ideal electrical characteristics and age only slightly towards lower barrier height values. Al---Ge contacts exhibit very pronounced ageing towards higher barrier height values, due to formation of an extra aluminium oxide interfacial layer. Because of this, the barrier height values of aged Al---Ge contacts derived from I-V and C-V characteristics differ significantly. The dependence of the barrier height, (φ_b) on the metal work function, φ_m, for different metal-germanium contacts shows that surface states play an important role in the formation of the barrier. The density of germanium surface states is estimated to be D_s = 2 × 10¹³ eV⁻¹ cm⁻².     

Metal-insulator transition in Sb-doped short period Si/SiGe superlattices

Low-temperature magnetotransport measurements (50 mK < T < 4.2 K) on Sb-doped short period Si/SiGe superlattices (d ≈ 40 Å) are presented. The experiments show evidence for single particle quantum interference and enhanced electron-electron interaction effects. Furthermore, for a Sb doping concentration of 4.5 × 10¹⁸ cm⁻³, a field induced metal to insulator transition (MIT) is observed for magnetic fields B parallel to the superlattice layers, whereas for the perpendicular direction of B, the MIT does not take place. The anisotropy and dimensionality of the SL-samples is discussed.     

Characterization of phosphorus implanted low pressure chemical vapor deposited polycrystalline silicon

Thin (3000–5000Å) low pressure chemically vapor deposited (LPCVD) films of polycrystalline silicon suitable for microelectronics applications have been deposited from silane at 600°C and at a pressure of 0.25 Torr. The films were phosphorus implanted at 150 KeV and electrically characterized with the annealing conditions and film thickness as parameters, over a resistivity range of four orders of magnitude (10³–10⁷Ω/□). Annealing during silox deposition was found to result in a lower film resistivity than annealing done in nitrogen atmosphere. Resistivity measurements as a function of temperature indicate that the electrical activation energy is a linear function of 1/N(N is the doping concentration), changing from 0.056 eV for a doping concentration of 8.9 × 10¹⁸ cm⁻³ to 0.310 eV for doping concentration of 3.3 × 10¹⁸ cm⁻³. The grain boundary trap density was found to have a logarithmically decreasing dependence on the polysilicon thickness, decreasing from 1.3 × 10¹³ cm⁻² for 2850Å polysilicon film to 8.3 × 10¹² cm⁻² for 4500Å polysilicon film.     

Measurement of low densities of surface states at the Si---SiO2-interface

By a careful process Si---SiO₂-interfaces can be made with a low oxide charge Q_ox and with a low surface states density N_ss. For dry oxides on (100) N_ss-values as low as a few 10⁹ cm⁻² eV⁻¹ are found on samples with an oxide charge density of 3·0 × 10¹⁰ cm⁻². Only the Nicollian-Goetzberger conductance method is proved to give reasonable results on these structures. The quasi-static low frequency C-V-technique is in good agreement with the conductance technique for samples with N_ss-values higher than 1·0 × 10¹⁰ cm⁻² eV⁻¹. The spatial fluctuation of surface potential, mainly caused by oxide charge fluctuations, is an important parameter when studying the high or low frequency C-V-characteristics. Some irregularities in the experimental N_ss-φ_s-curves are explained.     

Process and device characterization of high voltage gallium arsenide P-i-N layers grown by an improved liquid phase epitaxy method

GaAs P-i-N layers with an i-region net doping of less than 10¹² cm⁻³ were grown on P⁺ and N⁺ substrates by a modified liquid phase epitaxy (LPE) method. Doping profiles and structural data obtained by varius characterization techniques are presented and discussed. A P⁺-P-i-N-N⁺ diode with a 25 μm-wide i-region exhibits a breakdown voltage of 1000 V, a t_rr of 50 ns, and reverse current densities (at V_R = 800 V) of − 3 × 10⁻⁶ A/cm² at 25°C and 10⁻² A/cm² at 260° C.     

Selenium doped high-index GaAs epilayers grown by molecular beam epitaxy

Using elementary Se we grew Se-doped GaAs films on GaAs (111), (411), (711) and (100) substrates by molecular beam epitaxy. The films grown on all the high-index substrates showed n-type conduction and the maximum carrier concentration reached 2.1 × 10¹⁹ cm⁻³ for the film grown on the (411)B substrate. The carrier concentration began to saturate at a Se concentration near 10¹⁹ cm⁻³ but continued to increase up to a Se concentration of 2 × 10²⁰ cm⁻³. Above 2 × 10²⁰ cm⁻³ Se concentration, slow reduction of the carrier concentration was observed. We obtained excellent surface morphology when n-type GaAs films were grown on (411)A and (711)B substrates even at a Se concentration of 7 × 10²⁰ cm⁻³.     

High performance poly-crystalline silicon thin film transistorsfabricated using remote plasma chemical vapor deposition of SiO2

A remote plasma chemical vapor deposition (RPCVD) of SiO₂ was investigated for forming an interface of SiO₂/Si at a low temperature below 300°C. A good SiO₂/Si interface was formed on Si substrates through decomposition and reaction of SiH₄ gas with oxygen radical by confining plasma using mesh plates. The density of interface traps (D_it) was as low as 3.4×10¹⁰ cm^-2eV^-1. N- and p-channel Al-gate poly-Si TFTs were fabricated at 270°C with SiO₂ films as a gate oxide formed by RPCVD and laser crystallized poly-crystalline films formed by a pulsed XeCl excimer laser. They showed good characteristics of a low threshold voltage of 1.5 V (n-channel) and -1.5 V (p-channel), and a high carrier mobility of 400 cm²/Vs     

The physics and fabrication of in situ back-gated (311)A hole gas heterojunctions

This paper reports the fabrication of an in situ back-gated hole gas on the (311)A surface of GaAs. The hole density can be varied from fully depleted to p_s = 2.1 × 10¹¹ cm⁻² with mobilities of up to μ = 1.1 × 10⁶ cm²V⁻¹ s⁻¹. It is seen that for carrier densities down to p_s = 4 × 10¹⁰ cm⁻² the mobility in the [ ] direction is greater than that in the [ ] direction. Using a combination of front- and back-gates we are able to keep the carrier density constant and deform the hole gas wavefunction such that the holes are pushed up against or moved further away from the heterointerface. Thus we are able to separately investigate the various scattering mechanisms that determine the mobility, and compare the experimental data with theoretical calculations based on the shape of the wavefunction.     

Flicker-Noise Improvement in 100-nm $L_{g} hbox{Si}_{0.50}hbox{Ge}_{0.50}$ Strained Quantum-Well Transistors Using Ultrathin Si Cap Layer

This letter presents a record low flicker-noise spectral density in biaxial compressively strained p-channel 100-nm L_gSi_0.50Ge_0.50 quantum-well FETs (QWFETs) with ultrathin Si (~2 nm) barrier layer and 1-nm EOT hafnium silicate gate dielectric. The normalized power spectral density of I_d fluctuations (S_Id/I_d ²) in Si_0.50Ge_0.50 QWFETs exhibits significant improvement by ten times over surface channel unstrained Si pMOSFETs at high V_g due to strong confinement of holes within the high-mobility QW and strong quantization in the ultrathin Si barrier layer enabled by low-thermal-budget device processing. The noise behavior in strained QW devices is found to evolve from being correlated mobility fluctuation dominated across most of V_g range to being Hooge mobility fluctuation dominated at very high V_g.     

Transport of the photoexcited electron-hole plasma in InP

Transport properties of the photoexcited electron-hole plasma in n-type InP have been studied by the spatial-imaged, time-resolved Raman scattering technique with 30μm and 0.1μm spatial resolution for lateral and perpendicular transport, respectively, and on a picosecond time scale. The plasma density ranging from 1 × 10¹⁶ to 2 × 10¹⁷ cm⁻³ was deduced from fitting of the Raman spectra with the plasmon-LO phonon scattering theory which took into account the contributions from free holes. In contrast to the experimental results of Young and Wan who found that ordinary diffusion equation was sufficient to fit their transient plasma density-time profiles in semi-insulating InP, our experimental measurements have shown that perpendicular transport (i.e., expansion into the bulk crystal) of the plasma in n-type InP can be very well described by a modified diffusion equation including the effect of drifting away from the surface based on a hydrodynamic model. The transient plasma density-time profiles were studied at T = 300K and for an initial injected plasma density n 2 × 10¹⁷ cm⁻³. The plasma has been found to expand laterally at a velocity V 5 × 10⁴ cm/sec and perpendicularly into the crystal at a velocity Vp 1.5 × 10⁵ cm/sec.     

Low 1/f noise design of Hi-CMOS devices

Low-frequency noise characteristics of High-Performance CMOS(Hi-CMOS) devices were measured. It was found that the equivalent input noise power SVg,eqfor n-channel MOSFET's has a 1/fα spectrum (0.8 < α < 0.95) above 10 µA, even for sealed-down devices with channel lengths LGof 2 µm. The SVg,eqis clearly proportional to 1/Leffdown to 0.8 µm. The noise characteristics of p-channel and n-channel MOSFET's were compared. It was found that in Hi-CMOS devices, noise reduction in normally-off-type p-channel devices was obtained by light boron-ion implantations at doses below 10¹²cm^-2. The 1/f noise level of p-channel devices was reduced to 1/10- 1/20 that of n-channel devices. In n-channel devices, the low-frequency noise power is a slow increasing function of the drain current. In p-channel devices, on the other hand, a threshold current was observed at which the noise begins to increase rapidly. The results are discussed in this paper in relation to the theoretical model of 1/f noise. The device design for reducing 1/f noise in CMOS differential amplifiers is also examined.     

Low-frequency noise in Si0.7Ge0.3 surface channel pMOSFETs with ALD HfO2/Al2O3 gate dielectrics

Low-frequency noise was characterized in Si_0.7Ge_0.3 surface channel pMOSFETs with ALD Al₂O₃/HfO₂/Al₂O₃ stacks as gate dielectrics. The influences of surface treatment prior to ALD processing and thickness of the Al₂O₃ layer at the channel interface were investigated. The noise was of the 1/f type and could be modeled as a sum of a Hooge mobility fluctuation noise component and a number fluctuation noise component. Mobility fluctuation noise dominated the 1/f noise in strong inversion, but the number fluctuation noise component, mainly originating from traps in HfO₂, also contributed closer to threshold and in weak inversion. The number fluctuation noise component was negligibly small in a device with a 2 nm thick Al₂O₃ layer at the SiGe channel interface, which reduced the average 1/f noise by a factor of two and decreased the device-to-device variations.     

Hydrogen “doped” thin film diamond field effect transistors for high power applications

Early predictions that diamond would be a suitable material for high performance, high power devices were not supported by the characteristics of diodes and field effect transistors (FETs) fabricated on boron doped (p-type) thin film material. In this paper commercially accessible polycrystalline thin film diamond has been turned p-type by the incorporation of near surface hydrogen; mobility values as high as 70 cm² V⁻¹ s⁻¹ have been measured for films with a carrier concentration of 5×10¹⁷ cm⁻³. Schottky diodes and metal–semiconductor FETs (MESFETs) have been fabricated using this approach which display unprecedented performance levels; diodes with a rectification ratio >10⁶, leakage currents <1 nA, no indication of reverse bias breakdown at 100 V and an ideality factor of 1.1 have been made. Simple MESFET structures that are capable of switching V_DS values of 100 V with low leakage and current saturation (pinch-off) characteristics have also been fabricated. Predictions based upon experiments performed on these devices suggest that optimised device structures will be capable of operation at power levels up to 20 W mm⁻¹, implying that thin film diamond may after all be an interesting material for power applications.