MOS Capacitance-Voltage Characteristics Ⅲ.Trapping Capacitance from 2-Charge-State Impurities

Low-frequency and high-frequency capacitance-voltage curves of Metal-Oxide-Semiconductor Capacitors are presented to illustrate giant electron and hole trapping capacitances at many simultaneously present two-charge-state and one-trapped-carrier,or one-energy-level impurity species.Models described include a donor electron trap and an acceptor hole trap,both donors,both acceptors,both shallow energy levels,both deep,one shallow and one deep,and the identical donor and acceptor.Device and material parameters are selected to simulate chemically and physically realizable capacitors for fundamental trapping parameter characterizations and for electrical and optical signal processing applications.     

MOS Capacitance-Voltage Characteristics Ⅱ.Sensitivity of Electronic Trapping at Dopant Impurity from Parameter Variations

Low-frequency and high-frequency Capacitance-Voltage（C-V） curves of Metal-Oxide-Semiconductor Capacitors（MOSC）,including electron and hole trapping at the dopant donor and acceptor impurities,are presented to illustrate giant trapping capacitances,from>0.01C_ox to>10C_ox.Five device and materials parameters are varied for fundamental trapping parameter characterization,and electrical and optical signal processing applications.Parameters include spatially constant concentration of the dopant-donor-impurity electron trap,N_DD,the ground state electron trapping energy level depth measured from the conduction band edge, E_C—E_D,the degeneracy of the trapped electron at the ground state,g_D,the device temperature,T,and the gate oxide thickness,x_OX.     

Trapping and recombination processes via deep level T3 in semi-insulating gallium arsenide

Trapping and recombination of free carriers by deep level T₃ has been studied. Occupancy of the level by electrons and dynamics of its filling and emptying as a function of illumination with monoenergetic photons in 0.69–1.55 eV range has been monitored by the thermally stimulated currents method. We have found that level T₃ behaves more like a recombination center than like an ordinary electron trap. Besides trapping free electrons from conduction band, this trap can also communicate with valence band, trapping holes. The capture cross section for trapping a hole is estimated to be comparable or even larger than the capture cross section for trapping an electron. However, in many experimental conditions free electrons are generated more abundantly than free holes, and free carrier mobility and thermal velocity are both much higher for electrons than for holes. Therefore, electron trapping often prevails, so that this frequently detected defect, has been up to now most often perceived as a deep electron trap.     

Numerical simulation of the response of substrate traps to a voltage applied to the gate of a gallium arsenide field effect transistor

We report on a numerical simulation of the response of substrate traps to a voltage applied to the gate of a gallium arsenide field effect transistor (GaAs FET) using proprietary simulation software. The substrate is assumed to contain shallow acceptors compensated by deep levels. The ratio between the densities of deep and shallow levels is considered to be one hundred, which is a typical value for semi-insulating substrates. Although several traps may be present in the substrate but only the most commonly observed ones are considered, namely hole traps related to Cu and Cr, and the familiar native electron trap EL2. The current–voltage characteristics of the GaAs FET are calculated in the absence as well as in the presence of the above mentioned traps. It was found that the hole traps are affected by the gate voltage while the electron trap is not. This effect on the response of hole traps is explained by the fact that the quasi-hole Fermi level in the substrate is dependent on the gate voltage. However, the electron quasi-Fermi level in the substrate is insensitive to the gate voltage and therefore electron traps are not perturbed.     

Random telegraph signals in deep submicron n-MOSFET's

Random telegraph signals (RTS) in the drain current of deep-submicron n-MOSFET's are investigated at low and high lateral electric fields. RTS are explained both by number and mobility fluctuations due to single electron trapping in the gate oxide. The role of the type of the trap (acceptor or donor), the distance of the trap from the Si-SiO₂ interface, the channel electron concentration (which is set by the gate bias) and the electron mobility (which is affected by the drain voltage) is demonstrated. The effect of capture and emission on average electron mobility is demonstrated for the first time. A simple theoretical model explains the observed effect of electron heating on electron capture. The mean capture time depends on the local velocity and the nonequilibrium temperature of channel electrons near the trap. The difference between the forward and reverse modes (source and drain exchanged) provides an estimate of the effective trap location along the channel     

MOS Capacitance-Voltage Characteristics II. Sensitivity of Electronic Trapping at Dopant Impurity from Parameter Variations

Low-frequency and high-frequency Capacitance-Voltage (C-V) curves of Metal-Oxide-Semiconductor Capacitors (MOSC), including electron and hole trapping at the dopant donor and acceptor impurities, are presented to illustrate giant trapping capacitances, from > 0.01C_ox to > 10C_ox. Five device and materials parameters are varied for fundamental trapping parameter characterization, and electrical and optical signal processing applications. Parameters include spatially constant concentration of the dopant-donor-impurity electron trap, N_DD, the ground state electron trapping energy level depth measured from the conduction band edge, E_C-E_D, the degeneracy of the trapped electron at the ground state, g_D, the device temperature, T, and the gate oxide thickness, x_ox.     

Channel length influenced contribution of hole and electron trapping effect to threshold voltage stability in organic field effect transistors

Effect of channel length on hysteresis and threshold voltage shift in copper phthalocyanine (CuPc) based organic field effect transistors was studied. Contrary to expectation, longer channel length devices exhibited minimum threshold voltage shift. Influence of channel length on the contribution of hole and electron trapping to threshold voltage stability was determined. Shortest channel length devices exhibited highest electron trapping effect while longest channel devices exhibited minimum hole as well as electron trapping. Lower hole trap effect for longer channel length devices was suggested to be due to reduced longitudinal field between source and drain electrodes while minimum electron trapping was attributed to suppression of drain current by increased hole trap centres.     

2-D simulation of kink-related sidegating effects in GaAs MESFETs

Sidegating (backgating) effects in a planar structure with sidegate on the same side as MESFET are studied by two-dimensional simulation and the results are compared with those for a structure with a backgate on the back side of the substrate. The kink-related sidegating is reproduced in the planar structure, too. Its mechanism is discussed and is attributed to the change of EL2's role from an electron trap to a recombination center by capturing holes, which are generated by impact ionization and flow into the semi-insulating substrate including EL2 (deep donor). The dependence of shallow acceptor density in the semi-insulating substrate is also studied. It is shown that the kink-related sidegating is less remarkable in the case with lower acceptor density in the substrate. Potential dependence of sidegating effects on the sidegate (backgate) position is also discussed.     

Hole trapping and trap generation in the gate silicon dioxide

Oxide breakdown has been proposed to be a limiting factor for future generation CMOS. The breakdown is caused by defect generation in the oxide. Although electron trap generation has received much attention, there is little information available on the hole trap generation. The relatively high potential barrier for holes at the oxide/Si interface makes it difficult to achieve a high level of hole injection. Most previous work was limited to an injection level Q_inj of 10¹⁴ cm^-2. In this paper, we investigate the hole trapping and trap generation when Q_inj reaches the order of 10¹⁸ cm^-2. When Q_inj <10¹⁵ cm^-2, the trapping is dominated by the as-grown traps. As Q_inj increases further, however, it is found that the generation of new traps controls the trapping. The trap generation does not saturate up to the oxide breakdown. The trapping kinetics for both the as-grown and the generated traps is studied. The relationship between the density of generated traps and the Q_inj is explored. Attention is paid to how the trapping and trap generation depends on the distance from the interface. In contrast to the uniform generation of electron traps across the oxide, we found that the hole trap generation was not uniform and it moved away from the interface as Q_inj increased     

Charge trapping in ion-sputtered silicon dioxide films on silicon

Charge trapping in thermal silicon dioxide has been previously studied in great detail. Recently there has been an interest in depositing silicon dioxide films at lower temperatures to be compatible with device technologies that are not compatible with the higher temperature. This paper discusses the electron and hole trapping behavior in room temperature, ion-sputtered silicon dioxide thin films. Generally, these films are observed to trap both carriers much more efficiently then thermal silicon dioxide films. The trapping parameters such as the trap cross-section, location, density and the trapping efficiency are reported.     

Point Defects in Pb-, Bi-, and In-Doped CdZnTe Detectors: Deep-Level Transient Spectroscopy (DLTS) Measurements

We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48?eV. The absence of a V_Cd trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[Pb_Cd]⁺-V _Cd ^2? ]^?. Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36?meV and a deep donor trap at around 0.82?eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18?eV (A-centers) and 0.31?eV (V_Cd), and a deep trap at around 1.1?eV.     

Understanding Thermal and A-Thermal Trapping Processes in Lead Halide Perovskites Towards Effective Radiation Detection Schemes

Lead halide perovskites (LHP) are rapidly emerging as efficient, low-cost, solution-processable scintillators for radiation detection. Carrier trapping is arguably the most critical limitation to the scintillation performance. Nonetheless, no clear picture of the trapping and detrapping mechanisms to/from shallow and deep trap states involved in the scintillation process has been reported to date, as well as on the role of the material dimensionality. Here, this issue is addressed by performing, for the first time, a comprehensive study using radioluminescence and photoluminescence measurements side-by-side to thermally-stimulated luminescence (TSL) and afterglow experiments on CsPbBr₃ with increasing dimensionality, namely nanocubes, nanowires, nanosheets, and bulk crystals. All systems are found to be affected by shallow defects resulting in delayed intragap emission following detrapping via a-thermal tunneling. TSL further reveals the existence of additional temperature-activated detrapping pathways from deeper trap states, whose effect grows with the material dimensionality, becoming the dominant process in bulk crystals. These results highlight that, compared to massive solids where the suppression of both deep and shallow defects is critical, low dimensional nanostructures are more promising active materials for LHP scintillators, provided that their integration in functional devices meets efficient surface engineering.     

钒掺杂形成半绝缘6H-SiC的补偿机理

研究了钒掺杂生长半绝缘6H-SiC的补偿机理.二次离子质谱分析结果表明,非故意掺杂生长的6H-SiC中,氮是主要的剩余浅施主杂质.通过较深的钒受主能级对氮施主的补偿作用,得到了具有半绝缘特性的SiC材料.借助电子顺磁共振和吸收光谱分析,发现SiC中同时存在中性钒(V4 )和受主态钒(V3 )的电荷态,表明掺入的部分杂质钒通过补偿浅施主杂质氮,形成受主态钒,这与二次离子质谱分析结果相吻合.通过对样品进行吸收光谱和低温光致发光测量,发现钒受主能级在6H-SiC中位于导带下0.62eV处.     

Schottky-barrier capacitance measurements for deep level impurity determination

The time dependence of a Schottky-barrier capacitance due to thermal excitation of trapping centres has been studied. An expression for the junction capacitance is derived which is not restricted to any special range of reverse bias nor to a special relation between shallow and deep impurity concentration. The concentration ratio of shallow to deep centres is calculated from the values of the capacitance at zero and infinite time. From a capacitance vs. time plot the trap emission rate for electrons e_n is obtained. Their energetic level within the forbidden band-gap is determined from the temperature dependence of e_n as well as from the capacitance-time variation. Experimental studies which do confirm the calculations were carried out on gold contacts on oxygen-doped n-type GaAs. Representative results of the investigated samples were: shallow donor density 3 × 10¹⁵ cm^?3, trap density 9·8 × 10¹⁵ cm^?3, electron emission rate 6 × 10^?2 sec^?1, energetic level 0·68 eV and capture cross section 7 × 10^?16 cm².     

Carrier trapping in thin N2O-grown oxynitride/oxide di-layer for PowerMOSFET devices

A detailed study of the carrier trapping properties shown by the silicon/oxynitride/oxide gate layers in PowerVDMOS technologies is reported. A quantitative analysis of hole and electron trap densities versus the specific N₂O based nitridation process, extracted from Fowler–Nordheim constant current stress kinetics, allows a deep understanding of the role played by those defects in the susceptibility of every nitrided layer.     

Charge trapping in substoichiometric germanium oxide

Electron and hole trapping in substoichiometric germanium oxides are investigated through the use of hybrid density functionals. We consider disordered model structures generated by Monte-Carlo bond switching and by ab initio molecular dynamics (MD). The Monte-Carlo model consists of fourfold coordinated Ge atoms and of twofold coordinated O atoms, and does not show trap levels neither for electron nor for holes. At variance, the MD model shows threefold coordinated O and Ge atoms forming valence alternation pairs and is found to present trap states for both carriers. The trapping states correspond to the formation and breaking of Ge-Ge bonds. The associated defect levels are determined within a band diagram of the Ge/GeO₂ interface.     

Influence of alloy composition,substrate temperature,and doping concentration on electrical properties of Si-doped n-Alx Ga1−x As grown by molecular beam epitaxy

Capacitance and Hall effect measurements in the temperature range 10-300 K were performed to evaluate the deep and shallow level characteristics of Si-doped n-Al_xGa_-xAs layers with 0 × 0.4 grown by molecular beam epitaxy. For alloy compositions × 0.3 the overall trap concentration was found to be less than 10⁻² of the carrier concentration. In this composition range the transport properties of the ternary alloy are comparable to those of n-GaAs:Si except for lower electron mobibities due to alloy scattering. With higher Al content one dominant electron trap determines the overall electrical properties of the material, and in n-Al_0.35Ga_0.65As:Si the deep trap concentration is already of the order of the free-carrier concentration or even higher. For the composition × = 0.35 ± 0.02 the influence of growth temperature and of Si dopant flux intensity on the deep trap concentration, on shallow and deep level activation energy, and on carrier freeze-out behaviour was studied and analyzed in detail. Our admittance measurements clearly revealed that the previously assumed deepening of the shallow level in n-Al_x Ga_1-x As of alloy composition close to the direct-indirect cross-over point does actuallynot exist. In this composition range an increase of the Si dopant flux leads to a reduction of the thermal activation energy for electron emission from shallow levels due to a lowering of the emission barrier by the electric field of the impurities. The increasing doping flux also enhances the concentration of the dominant electron trap strongly, thus indicating a participation of the dopant atoms in the formation of deep donor-type (D,X) centers. These results are in excellent agreement with the model first proposed by Lang et al. for interpretation of deep electron traps in n-Al_x Ga_1-x grown by liquid phase epitaxy.     

Evidence of surface states for AlGaN/GaN/SiC HEMTs passivated Si<Subscript>3</Subscript>N<Subscript>4</Subscript> by CDLTS

In AlGaN/GaN heterostructure field-effect transistors (HEMTs) structures, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current and low frequency noise. This work demonstrates the effect of surface passivation on the current-voltage characteristics and we report results of our investigation of the trapping characteristics of Si₃N₄-passivated AlGaN/GaN HEMTs on SiC substrates using the conductance deep levels transient spectroscopy (CDLTS) technique. From the measured of CDLTS we identified one electron trap had an activation energy of 0.31 eV it has been located in the AlGaN layer and two hole-likes traps H ₁, H ₂. It has been pointed out that the two hole-likes traps signals did not originate from changes in hole trap population in the channel, but reflected the changes in the electron population in the surface states of the HEMT access regions.     

Investigation of oxide charge trapping and detrapping in a MOSFETby using a GIDL current technique

We proposed a new measurement technique to investigate oxide charge trapping and detrapping in a hot carrier stressed n-MOSFET by measuring a GIDL current transient. This measurement technique is based on the concept that in a MOSFET the Si surface field and thus GIDL current vary with oxide trapped charge. By monitoring the temporal evolution of GIDL current, the oxide charge trapping/detrapping characteristics can be obtained. An analytical model accounting for the time-dependence of an oxide charge detrapping induced GIDL current transient was derived. A specially designed measurement consisting of oxide trap creation, oxide trap filling with electrons or holes and oxide charge detrapping was performed. Two hot carrier stress methods, channel hot electron injection and band-to-band tunneling induced hot hole injection, were employed in this work. Both electron detrapping and hole detrapping induced GIDL current transients mere observed in the same device. The time-dependence of the transients indicates that oxide charge detrapping is mainly achieved via field enhanced tunneling. In addition, we used this technique to characterize oxide trap growth in the two hot carrier stress conditions. The result reveals that the hot hole stress is about 10⁴ times more efficient in trap generation than the hot electron stress in terms of injected charge     

Hole trapping in E-beam irradiated SiO2 films

Low energy (25 kV) electron beam irradiation of MOS capacitors is shown to produce neutral hole traps in thin ‘radiation hardened’ SiO₂ films. These traps are found in an uncharged state after irradiation and are populated by passing a small hole current, generated by avalanche breakdown of then-type silicon substrate, through the oxide. From the time dependence of the observed trapping, a capture cross-section between 1 × 10∼⁻¹³ and 1 × 10⁻¹⁴ cm² is deduced. The trap density is found to depend on the annealing conditions and incident electron beam dosage. The density of traps increases with incident electron beam exposure. Once introduced into the oxide by the radiation the traps can be removed by thermal anneals at temperatures above 500° C. Parallels between electron and hole trapping on these neutral centers are strong evidence for an amphoteric uncharged trap generated by ionizing radiation.