Nonuniform Doping Profile Research Articles

High Linearity InGaP/GaAs Power HBTs by Collector Design

Improved power linearity of InGaP/GaAs heterojunction bipolar transistors (HBTs) with collector design is reported. The collector design is based on nonuniform collector doping profile which is to employ a thin high-doping layer (5/spl times/10/sup 17/ cm/sup -3//200 /spl Aring/) inside the collector (1/spl times/10/sup 16/ cm/sup -3//7000 /spl Aring/). The additional thin high-doping layer within the collector shows no obvious effects and impacts in dc characteristics and device fabrication if the layer was inserted close to the subcollector. For an HBT with a thin high-doping layer being inserted 4000 /spl Aring/ from the base-collector junction, the experimental result on third-order intermodulation demonstrates the significant reduction by as large as 9 dBc and improved IIP3 by 5 dB under input power of -10 dBm at frequency of 1.8 GHz.

Effect of nonuniform doping profile on thermometric performance of diode temperature sensors

A theoretical investigation of the influence of a nonuniform doping concentration to the temperature response curve of diode temperature sensors is presented, which is the first effort in this field important for diffused diodes used as the temperature sensors. The current- voltage characteristic, from which the temperature response curve can be obtained, has been calculated using the model of a one-dimensional exponentially graded pnn junction with uniformly doped base region and the diffusion current of the minority carriers through the pnn junction. We show that depending on the doping gradient both contributions to the current coming from the electron and hole current components appear to be of the same order of magnitude. That is in contrast to the prediction of the widely used asymmetrical step junction model. It follows from numerical calculations that an effective shift of the tempera- ture response curve due to nonuniformly doped emitter region in the temperature equivalent can reach the value of about 20 K. The limiting temperature Tm in the temperature response curve that restricts its extent into the high temperature range has been analyzed depending on the excitation current, the doping concentration of the base, and the pnn junction depth.

Enhancement of device performance in vertical sub-100 nm MOS devices due to local channel doping

For future devices in metal oxide semiconductor technology there is a great interest in down scaling of device dimensions to improve device performance and to increase packing density. New device designs with nonuniform channel doping profiles are investigated to further enhance performance over conventional device designs and to suppress short channel effects. In this work we report sub-100 nm MOS devices with channel delta doping profiles grown using molecular beam epitaxy. Electrical characteristics and carrier transport in these devices are investigated and show significant improvements compared to conventional devices. Sharp channel profiles facilitate control of electric field and this “field engineering” improve the breakdown characteristics and provide better control of threshold voltage.

Effect of substrate doping profile onC−Vcurves for thin MOS capacitors

We use a full quantum model of MOS (metal oxide semiconductor) structure to study the influence of a non-uniform doping profile of the substrate on the capacitance-voltage ( C − V ) behavior of the structure. For different “realistic” doping profiles, simulations are performed and compared to simulations with an uniform doping and to C − V measurements for samples with oxide thickness in the range [2−5 nm] [1]. In each case, we have extracted the oxide thickness that is found to be independent of the doping and the flat-band voltage which can be shifted up to 200 mV regarding the different profiles tested here. Moreover, below about 3 nm, the shape of the C − V simulation is more affected, which shows that the doping profile of the substrate has a great importance for an accurate C − V modeling of ultra-thin MOS structures.

An improved time domain analysis of the charge pumping current

A new time domain analysis of the charge pumping phenomenon in metal-oxide-semiconductor field-effect transistors is presented. With this theoretical approach we model the traps filling and the charge pumping current with any gate signal waveform and any energy distribution of the interface traps in the semiconductor bandgap. A method is also presented for the determination of the energy levels reached at the end of the non-steady-state emission of electrons and holes. The theoretical charge pumping response of a single trap is also investigated for uniform and non-uniform substrate doping profiles.

Quasi-two-dimensional subthreshold current model of deep submicrometer SOI drive-in gate controlled hybrid transistors with lateral non-uniform doping profile

We have analyzed the operating mechanism of the novel deep submicrometer SOI drive-in gate controlled hybrid transistor (DGCHT), which can effectively alleviate the contradiction between speed enhancement and power reduction in conventional MOS devices and can improve the output resistance. On the basis of this, the subthreshold current model of DGCHTs is proposed. The model takes into account the impact of lateral non-uniform doping profile on body effect, short-channel effect and carrier mobility. Considering the mobile charge, two-dimensional Poisson equation is solved with quasi-two-dimensional analysis and parabolic approximation of surface potential. With the surface potential obtained, the subthreshold current is figured out, including both the diffusion and drift component. The calculated results are in good agreement with the MEDICI numerical simulation results, indicating the correct description of the current characteristics of SOI DGCHT by the presented model. The model can also be considered as an important reference to the current simulation of deep submicrometer MOSFET with pocket implantation.

Reduction of UHF power transistor distortion with a nonuniform collector doping profile

The linearity of a class-A, bipolar UHF power transistor is investigated. The device is intended for transmission of signals with multiple (TV) channels. Mixing between the various channels must be suppressed, which makes linearity an important parameter. This paper presents a novel approach, where process technology is specifically optimized to minimize distortion. It is shown that particularly the nonlinear collector-base capacitance strongly affects the linearity of this type of device. With a modified collector-base doping profile, the capacitance is manipulated. A nonuniform profile is introduced that significantly reduces third-order intermodulation. The profile consists of an arsenic doped spike that is grown epitaxially into the (otherwise) lightly doped collector. This reduces the bias dependence of C/sub cb/ and improves the tradeoff between linearity and breakdown or ruggedness. The reduction in third-order intermodulation is demonstrated both experimentally and by mixed-level MDS/MAIDS simulations.

Light dependence of SOI MOSFET with nonuniform doping profile

The light dependence of a fully depleted short channel silicon-on-insulator (SOI) MOSFET is investigated. As the photon flux density increases, there is a lowering in the surface potential barrier called the photon induced barrier lowering (PIBL). The threshold voltage shows a logarithmic reduction with the increase in the incident flux density. The drain source current and the transconductance significantly increase under the incident optical flux density. The device will be useful for high speed application in optical systems.

Modelling of heterojunction acoustic charge transport devices

A method of modelling heterojunction acoustic charge transport (HACT) in GaAs has been developed. This model allows for nonuniform impurity doping profile, variable epitaxial layer configuration, and arbitrary structural design of the input electrode. The acoustic wave potential is incorporated as a time- and space-varying doping density that adds directly to the impurity doping density. The wave-induced doping density is obtained from the piezoelectric displacement charge that accompanies the acoustic wave. The method uses a solution of the two-dimensional Poisson equation to obtain the potential and charge distribution in the charge injection region of an HACT device.

A better insight into the performance of silicon BJTs featuring highly nonuniform collector doping profiles

This paper investigates the effects of highly nonuniform collector doping profiles on the speed and breakdown performance of silicon bipolar transistors. Monte Carlo and drift diffusion simulation results point out that a thin highly doped layer adjacent to the base collector junction can improve the device cut off frequency without deteriorating significantly the maximum oscillation frequency and the breakdown voltage, provided the voltage drop across this layer is lower than an effective threshold of approximately 1.2 V. Guidelines are given for choosing the doping, position, and thickness of this layer.

Kinetic approach to barrier capacitance calculation and its application to modelling of microstructures with metal-semiconductor junctions

Non-uniform doping profiles are typical of modern microstructures. The conventional procedure used in computer simulation of capacitance-voltage (C-V) characteristics and C-V profiling is a quasistatic method based on solving a nonlinear Boltzmann-Poisson equation. This method includes the free carrier thermal motion, which is very important for microstructures. At the same time, it is strictly formal and employs numerical derivatives. From a mathematical standpoint, it is an ill-posed problem. To eliminate the disadvantages of the method, we propose another theoretical approach to barrier capacitance, inspired by two sources: small-signal modelling of the capacitor response and an averaging method for calculating values used in physical kinetics. This kinetic approach permits closer physical analysis of the C-V characteristics. Furthermore, the computer simulation technique based on this approach offers a great advantage over the quasistatic method in accuracy and efficiency. The results of computer simulation demonstrate the possibility of developing a technique for forward and inverse modelling.

Analysis of the depletion layer of exponentially graded p-n junctions with nonuniformly doped substrates

A detailed analysis of the depletion layer of exponentially graded p-n junctions is presented, which improves previous efforts in this field in different aspects. (1) We obtain analytical expressions for the depletion layer widths which are nearly as simple as those given by the widely used step and linearly graded junction models, but by far more accurate. In addition, we derive simple closed-form expressions for the punch-through and reach-through voltages. (2) The analysis is extended to the ease of substrates with nonuniform doping profiles, a case rarely treated in the literature, but of great importance for the design of many devices.

Study of Vacancy and Impurity Complexes in Si Solid-Phase Epitaxial Crystallization with Positron Annihilation Spectroscopy

AbstractWe investigate the residual vacancy defect species after crystallization of amorphous Si (a-Si) by solid phase epitaxy (SPE). To this end, we correlate the total and electronically-active doping concentrations measured by secondary mass spectrometry and spreading resistance analysis, and data from positron annihilation spectroscopy (PAS), which is sensitive to openvolume defects. Float-zone silicon substrates were implanted with boron, phosphorus and both phosphorus and boron ions to create nonuniform doping profiles at degenerate doping levels, after an amorphization step by 29Si+ ions. Samples were vacuum annealed at 600°C to induce SPE, and the SPE rate was measured by time-resolved reflectivity. PAS was used for identification of the impurity-defect complexes. Momentum-resolved PAS measurements enable the detection of phosphorus-vacancy (P-V) and oxygen-vacancy (O-V) complexes.

Numerical simulation of implanted top-gate 6H–SiC JFET characteristics

A detailed numerical analysis of implanted top-gate 6H–SiC JFET structures was performed revealing the influence of a non-uniform channel doping profile. Based on structural parameters extracted from simulations of the device characteristics at various bias conditions and temperatures, we obtain channel mobility parameters close to Hall data for bulk epitaxial layers.

Analytical threshold voltage model for ultrathin SOI MOSFETs including short-channel and floating-body effects

Short-channel effects (SCE) in ultrathin silicon-on-insulator (SOI) fully depleted (FD) MOSFETs are analyzed and an analytical model for threshold voltage, including the kink effect, is presented. The proposed model accounts for (1) a general nonuniform channel doping profile, (2) the drain-induced V/sub th/- lowering enhancement resulting from the interaction of (a) impact ionization, (b) floating-body, and (c) parasitic-bipolar effects. Good agreement between the proposed model and experimental data is demonstrated. Impact ionization and floating-body effects dominate V/sub th/ lowering for drain voltages larger than V/sub dk//spl sime/B/sub i/./spl lambda//sub i//3, where B/sub i/ is the impact ionization coefficient, and /spl lambda//sub i/ is the impact ionization length, a structural parameter which, for a single-drain SOI MOSFET, coincides with the SCE characteristic length /spl lambda/.

Modelling of collector signal delay effects in bipolar transistors

A detailed analysis of distributed delay effects related to carrier transport in the collector space-charge region is presented. The analysis is based on the extension of a recent formulation of minority-carrier transport in the base region which applies to nonuniform doping profiles and arbitrary injection levels. It is shown that these effects can be easily included in compact models by modifying the expression of the model parameters. Closed form analytical expressions for the forward transit time, base charge-partitioning factor and excess phase-shift time constant are derived, and the relevance of delay effects in the collector space-charge region is investigated in detail.

Doping dependence of the mobility enhancement in surface-channel strained-Si layers

In this paper we present simulation results for the doping dependence of the mobility enhancement in surface-channel strained-Si layers grown on relaxed Si1-xGex buffers. Our numerical results show that there is a significant reduction of the mobility enhancement with increasing substrate doping. At first, this result questioned the performance increase in devices based on these novel Si-based heteroepitaxy concepts when scaled to deep-submicron dimensions. However, we find that this is not really a problem since in devices with non-uniform doping profiles, representative of the state-of-the-art technology, significant mobility enhancement is still observed.

A discussion on the universality of inversion layer mobility in MOSFET's

An obvious discrepancy exists in published research results concerning the universality of MOS inversion layer electron mobility in nonuniform substrate doping profile cases. By thorough analysis of the data and the parameter extraction method, it is demonstrated that the discrepancy is simply due to the different definition of depletion layer charge and the invalid extraction of parameters from experimental data. Studies in this work show that inversion layer carrier mobility experiences the same universality feature in nonuniform doping substrates as in uniform ones.

Analytical model for dc drain current-voltage relationship in double-diffused channel of DMOS transistor

An analytical model for the dc current-voltage relationship in a double-diffused channel with a lateral nonuniform doping profile of a DMOS transistor has been developed. The equations are similar forms to the current-voltage equations of a conventional MOS transistor. The velocity saturation effect and the mobility reduction effect caused by a perpendicular electric field are also included. The model was verified by comparison with the results of two-dimensional numerical simulation and the fabricated device with a good agreement. The proposed model in this paper can be very useful for designing and analysing power devices with a double-diffused channel structure.

Thermoelectric and magnetotransport properties of Bi1-xSbx thin films and Bi/CdTe superlattices

The magnetotransport properties of Bi1-xSbx thin films (x = 0, 0.09 and 0.16) and Bi/CdTe superlattices have been determined by applying the quantitative mobility spectrum analysis (QMSA) and multicarrier fitting to the magnetic-field-dependent resistivities and Hall coefficients, using algorithms which account for the strong anisotropy of the mobilities. The experimentally derived electron and hole densities and mobilities are then used as the input to a nonparabolic and anisotropic band model that derives the thermal occupations and relaxation times for L-valley electrons and holes as well as T-valley and H-valley holes. This allows a calculation of the thermoelectric properties for comparison with experimental results. While the data for a Bi thin film and Bi/CdTe superlattices are reproduced quite well without any adjustable parameters, for Bi1-xSbx thin films a non-uniform doping profile must be assumed.