Schottky contact barrier height enhancement on p-type silicon by wet chemical etching

A wet chemical etch preceding the usual cleaning process has been found to yield Schottky barriers of high values on p-type silicon. This procedure produces a passivated surface layer which has resulted in Al/0-Si Schottky diodes with barrier height of 0.75 eV and ideality factor of 1.15. Measurements have confirmed the presence of electrically active donor-like states in this surface layer. The origin of the donor states is explained in terms of the deactivation of the boron acceptor by the formation ofH ⁺ B ^– pairs.     

The effect of incidence angle on disorder production in ion implanted Si

Abstract

Ne, Ar, Sb, and Xe ions have been implanted, at 30 keV or 80 keV and at various incidence angles, into Si substrates maintained at room temperature during implantation. Implantation-induced Si disorder was measured using RBS-channelling. The effects upon disorder of various incidence angles were studied over a fluence range of 10¹²-10¹⁶ ions·cm^?2.

The results show that, at low fluences the lighter (Ne) and slightly heavier (Ar) ion implantations generate a bimodal disorder-depth profile, whilst at higher fluences measurements of amorphised layer thickness as a function of ion incidence angle allow values of the standard deviation of the disorder profile parallel and transverse to the ion beam direction for each ion to be obtained with good agreement to theoretical predictions.     

Sputter damage in Si surface by low energy Ar+ ion bombardment

The damage distributions in Si(1 0 0) surface after 1.0 and 0.5 keV Ar⁺ ion bombardment were studied using MEIS and Molecular dynamic (MD) simulation. The primary Ar⁺ ion beam direction was varied from surface normal to glancing angle. The MEIS results show that the damage thickness in 1.0 keV Ar ion bombardment is reduced from about 7.7 nm at surface normal incidence to 1.3 nm at the incident angle of 80°. However, the damage thickness in 0.5 keV Ar ion bombardment is reduced from 5.1 nm at surface normal incidence to 0.5 nm at the incident angle of 80°. The maximum atomic concentration of implanted Ar atoms after 1 keV ion bombardment is about 10.5 at% at the depth of 2.5 nm at surface normal incidence and about 2.0 at% at the depth of 1.2 nm at the incident angle of 80°. However, after 0.5 keV ion bombardments, it is 8.0 at% at the depth of 2.0 nm for surface normal incidence and the in-depth Ar distribution cannot be observable at the incident angle of 80°. MD simulation reproduced the damage distribution quantitatively.     

高电荷态离子$lt;sup$gt;126$lt;/sup$gt;Xe$lt;sup$gt;$lt;i$gt;q$lt;/i$gt;+$lt;/sup$gt;引起GaN表面形貌变化研究

用不同电荷态的¹²⁶Xe^q+离子（9≤q≤30）在室温下轰击GaN晶体表面,经原子力显微镜分析表明,当q>18,辐照区域由隆起转为显著的刻蚀.被轰击后的GaN晶体表面形貌主要取决于入射离子的电荷态.同时,样品表面形貌还与入射离子的剂量和入射角有关;在实验参数范围,与入射离子的初动能没有明显关系（180 keV≤E_k≤600 keV）.当入射离子的电荷态q=18,与样品表面法线成60°角倾斜入射和垂直表面入射时,样品的表面几乎没有变化,只是倾斜入射后有很微小的隆起;当q＜18时,样品表面膨胀隆起,粗糙度增强,倾斜入射时表面隆起比垂直入射时更明显,而且都有清晰的峰状分界区;当q＞18时,样品表面被蚀刻呈凹陷状,有明显的齿状刻痕,且侵蚀深度与离子剂量近似呈线性关系,倾斜入射时的刻蚀深度大于垂直入射时的刻蚀深度. 关键词： 高电荷态离子 GaN晶体 原子力显微镜 表面形貌     

Shallow surface etching of organic and inorganic compounds by electrospray droplet impact

The electrospray droplet impact (EDI) was applied to bradykinin, polyethylene terephthalate (PET), SiO₂/Si, and indium phosphide (InP). It was found that bradykinin deposited on the stainless steel substrate was ionized/desorbed without the accumulation of radiation products. The film thickness desorbed by a single collisional event was found to be less than 10 monolayers. In the EDI mass spectra for PET, several fragment ions were observed but the XPS spectra did not change with prolonged cluster irradiation. The etching rate for SiO₂ by EDI was measured to be ∼0.2 nm/min. The surface roughness of InP etched by EDI was found to be one order of magnitude smaller than that etched by 3 keV Ar⁺ for about the same etching depths. EDI is capable of shallow surface etching with little damage left on the etched surface.     

The effect of incident angle on the C60 bombardment of molecular solids

The effect of incident angle on the quality of SIMS molecular depth profiling using C₆₀⁺ was investigated. Cholesterol films of ∼300 nm thickness on Si were employed as a model and were eroded using 40 keV C₆₀⁺ at an incident angle of 40° and 73° with respect to the surface normal. The erosion process was characterized by determining at each angle the relative amount of chemical damage, the total sputtering yield of cholesterol molecules, and the interface width between the film and the Si substrate. The results show that there is less molecule damage at an angle of incidence of 73° and that the total sputtering yield is largest at an angle of incidence of 40°. The measurements suggest reduced damage is not necessarily dependent upon enhanced yields and that depositing the incident energy nearer the surface by using glancing angles is most important. The interface width parameter supports this idea by indicating that at the 73° incident angle, C₆₀⁺ produces a smaller altered layer depth. Overall, the results show that 73° incidence is the better angle for molecular depth profiling using 40 keV C₆₀⁺.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Analysis of thermionic emission from electrodeposited Ni–Si Schottky barriers

Ni–Si Schottky barriers are fabricated by electrodeposition using n on n+ Si substrates. I–V, C–V and low temperature I–V measurements are presented. A high-quality Schottky barrier with extremely low reverse leakage current is revealed. The results are shown to fit an inhomogeneous barrier model for thermionic emission over a Schottky barrier proposed by Werner and Guttler [J.H. Werner, H.H. Guttler, Barrier inhomogeneities at Schottky contacts, J. Appl. Phys. 69 (3) (1991) 1522–1533]. A mean value of 0.76 V and a standard deviation of 66 mV is obtained for the Schottky barrier height at room temperature with a linear bias dependence. X-ray diffraction and scanning electron microscopy measurements reveal a polycrystalline Ni film with grains that span from the Ni–Si interface to the top of the Ni layer. The variation in Ni orientation is suggested as a possible source of the spatial distribution of the Schottky barrier height.     

Efficiency of excitation of space-charge waves in a thin-film semiconductor structure with a single strip Schottky barrier

Results of a theoretical analysis of the influence of various factors on the efficiency of excitation of space-charge waves in thin-film semiconductor structures by a single strip Schottky barrier are presented. It is shown that to increase the efficiency of conversion of a microwave signal into space-charge waves, it is advisable to use a Schottky barrier with a small contact potential with optimized values of the width of the Schottky barrier and the electron concentration in the film. Zh. Tekh. Fiz. 69, 128–130 (January 1999)     

Photovoltaic effect and optical absorption in MoS2

An investigation of the Schottky barriers of a number of metals on natural P-type MoS₂ was undertaken. The spectral dependence of the photovoltaic effect of all the metal barriers show two distinct features at 1.38 and 1.68 eV below the direct bandgap at 1.8 eV. A low energy edge at 1.2 eV is invariably observed for metal barriers on MoS₂. Absorption measurements performed over the same energy range indicate that the features observed in the photoresponse spectra are related to indirect transitions in MoS₂, in agreement with recent band calculations. Preliminary data indicate that MoS₂ based Schottky barrier solar cells may be of interest.     

Excitons in ZnP2 crystals in the electric field of a Schottky barrier

A study is made of the effect of electric fields on the exciton states of β-ZnP₂ crystals (T=77 K) in structures with Schottky barriers formed by depositing semitransparent electrically-conducting InSnO₂ films on the crystal surface. The observed changes in the exciton optical reflection spectra when an electrical potential is applied to a barrier are explained by the shift and broadening of the exciton level caused by the Stark effect. The experimental data are compared with calculations based on a theory of exciton optical reflection from planar spatially nonuniform structures. Fiz. Tverd. Tela (St. Petersburg) 40, 884–886 (May 1998)     

Ion beam modification of silicide-silicon interfaces

We have modified the contact interface between Pd₂Si and n-Si by ion implantation and investigated the effect of the implantation on Schottky barrier height and rate of silicide formation by electrical current-voltage measurements and Rutherford backscattering spectroscopy. Various ions, As. P, B. O and Si at 50 keV and up to a dose of 5 × 10¹⁴ ions/cm² were implanted into Si wafers before the Pd-deposition to form Pd₂Si. In the case of As and P, the implantation showed a large erect on the subsequent Pd₂Si formation; the formation is enhanced in the as-implanted samples, but it is retarded if an annealing at 600°C precedes the Pd-deposition. Silicide formation was found generally to help reduce the implantation damage (with or without the 600°C annealing) and showed improvements on the electrical characteristics of the contact interface. Consumption of the entire implanted region by silicide formation is found necessary for obtaining a good diode performance. In the case of As implantation, a lowering of the Schottky barrier height of Pd₂Si has been observed.     

低能氩离子束对多孔铝阳极氧化膜表面的刻蚀效应研究

用低能氩离子束(Ar⁺)处理了多孔铝阳极氧化膜(AAO)表面.扫描电子显微镜和原 子力显微镜结果表明，Ar⁺束刻蚀不仅可以有效地去除AAO反面阻挡层，还可使A AO表面产生多种特殊的形貌，如采用倾角入射可使其表面产生波纹，倾角入射同时旋转样品 台，可实现表面抛光.并结合Bradley和Harper提出的无定形材料表面波纹的形成和演化理论 解释了AAO表面波纹的特征. 关键词： 多孔铝阳极氧化膜 离子束刻蚀     

Schottky-type grain boundaries in CCTO ceramics

In this work we studied electrical barriers existing at CaCu₃Ti₄O₁₂ (CCTO) ceramics using dc electrical measurements. CCTO pellets were produced by solid state reaction method and X-ray diffractograms showed which single phase polycrystalline samples were obtained. The samples were electrically characterized by dc and ac measurements as a function of temperature, and semiconductor theory was applied to analyze the barrier at grain boundaries. The ac results showed the sample’s permittivity is almost constant (10⁴) as function of temperature at low frequencies and it changes from 100 to 10⁴ as the temperature increases at high frequencies. Using dc measurements as a function of temperature, the behavior of barriers was studied in detail. Comparison between Schottky and Poole-Frenkel models was performed, and results prove that CCTO barriers are more influenced by temperature than by electric field (Schottky barriers). Besides, the behavior of barrier width as function of temperature was also studied and experimental results confirm the theoretical assumptions.     

Application of mechanical scanning to ion implantation

Abstract

Atomic depth profiles from Be-implanted Si have been examined as a function of implant fluence and annealing, and the results have been correlated with theoretically calculated implantation induced damage profiles. The Be atomic depth profiles were obtained by secondary ion mass spectrometry (SIMS) techniques from samples implanted at 300 keV to fluences ranging from 2 × 10¹² to 10¹⁵ cm^?2. Subsequent to annealing at 600°C for 30 min, the Be SIMS profiles exhibited anomalous redistribution effects. The Be profiles obtained from the annealed samples had the same general features as the depth distribution of implant energy deposited into damage, based on Brice's¹ calculations. The correlation of the SIMS atomic profiles and the theoretical damage profiles indicated that Be “decorates” the implantation induced damage regions while redistributing during the annealing process.     

MC computer simulations of the preferential sputtering of Si-Ge alloys

Abstract

The ability of MC codes to predict the preferential sputtering of compound targets is investigated. The DYNA and TRIDYN codes are run for 3 keV Ar ⁺ bombardment of a SiGe binary target. The preferential sputtering of Si and Ge, the depth dependence of the sputter cross-section and the relocation operators are calculated. Difficulties arise in trying to reproduce the experimentally reported absence of preferentiality in the sputtered flux. The models used for the surface barriers, as well as the barrier heights, influences strongly the predicted quantities. A spherical surface barrier predicts much closer to stoichiometric fluxes than a planar barrier. Different codes give different collisional diffusivities for the target species in the bulk. The need for further experiments is stressed if some guidance in the choice of input parameters in the codes is desired.     

The modulation of Schottky barrier height of NiSi/n-Si Schottky diodes by silicide as diffusion source technique

This paper reports that the Schottky barrier height modulation of NiSi/n-Si is experimentally investigated by adopting a novel silicide-as-diffusion-source technique, which avoids the damage to the NiSi/Si interface induced from the conventional dopant segregation method. In addition, the impact of post-BF₂ implantation after silicidation on the surface morphology of Ni silicides is also illustrated. The thermal stability of Ni silicides can be improved by silicide-as-diffusion-source technique. Besides, the electron Schottky barrier height is successfully modulated by 0.11~eV at a boron dose of 10¹⁵~cm^-2 in comparison with the non-implanted samples. The change of barrier height is not attributed to the phase change of silicide films but due to the boron pile-up at the interface of NiSi and Si substrate which causes the upward bending of conducting band. The results demonstrate the feasibility of novel silicide-as-diffusion-source technique for the fabrication of Schottky source/drain Si MOS devices.     

Electrical characteristics of Pt/Au Schottky contacts to plasma-etched Al0.45Ga0.55N

The effects of inductively coupled plasma (ICP) etching on electrical properties of Pt/Au–Al_0.45Ga_0.55N Schottky contacts are investigated. There are two linear parts in the ln I–V curves of ICP-etched Schottky contacts at small forward currents at 198–298 K. Thermionic field emission (TFE) theory analysis shows that Schottky contact with ICP etching has much lower barrier height and higher tunnel transmission probability than that without ICP etching, which could be attributed to plasma damage introduced on the ICP-etched surface. The down linear part is probably connected to surface tunneling component originated from plasma-etched surface which joins Schottky area to Ohmic area.     

Thermal activation of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height

This paper investigates the thermal activation behaviour of current in an inhomogeneous Schottky diode with a Gaussian distribution of barrier height by numerical simulation. The analytical Gaussian distribution model predicted that the I--V--T curves may intersect with the possibility of the negative thermal activation of current, but may be contradictory to the thermionic emission mechanism in a Schottky diode. It shows that the cause of the unphysical phenomenon is related to the incorrect calculation of current across very low barriers. It proposes that junction voltage V_j, excluding the voltage drop across series resistance from the external bias, is a crucial parameter for correct calculation of the current across very low barriers. For correctly employing the thermionic emission model, V_j needs to be smaller than the barrier height Ф. With proper scheme of series resistance connection where the condition of V_j > Ф is guaranteed, I--V--T curves of an inhomogeneous Schottky diode with a Gaussian distribution of barrier height have been simulated, which demonstrate normal thermal activation. Although the calculated results exclude the intersecting possibility of I--V--T curves with an assumption of temperature-independent series resistance, it shows that the intersecting is possible when the series resistance has a positive temperature coefficient. Finally, the comparison of our numerical and analytical results indicates that the analytical Gaussian distribution model is valid and accurate in analysing I--V--T curves only for small barrier height inhomogeneity.     

Schottky barrier MOSFET structure with silicide source/drain on buried metal

In this paper, we propose a novel Schottky barrier MOSFET structure, in which the silicide source/drain is designed on the buried metal (SSDOM). The source/drain region consists of two layers of silicide materials. Two Schottky barriers are formed between the silicide layers and the silicon channel. In the device design, the top barrier is lower and the bottom is higher. The lower top contact barrier is to provide higher {on-state} current, and the higher bottom contact barrier to reduce the off-state current. To achieve this, ErSi is proposed for the top silicide and CoSi₂ for the bottom in the n-channel case. The 50~nm n-channel SSDOM is thus simulated to analyse the performance of the SSDOM device. In the simulations, the top contact barrier is 0.2e~V (for ErSi) and the bottom barrier is 0.6eV (for CoSi₂. Compared with the corresponding conventional Schottky barrier MOSFET structures (CSB), the high on-state current of the SSDOM is maintained, and the off-state current is efficiently reduced. Thus, the high drive ability (1.2mA/μm at V_ds=1V, V_gs=2V) and the high I_on/I_min ratio (10⁶) are both achieved by applying the SSDOM structure.