Function Of Junction Depth Research Articles

Junction Depth Dependence of the Gate Induced Drain Leakage in Shallow Junction Source/Drain-Extension Nano-CMOS

This study describes the dependence of the surface electric field to the junction depth of source/drain-extension, and the suppression of gate induced drain leakage (GIDL) in fully depleted shallow junction gate-overlapped source/drain-extension (SDE). The GIDL can be reduced by reducing shallow junction depth of drain-extension. Total space charges are a function of junction depth in fully depleted shallow junction drain-extension, and the surface potential is proportional to these charges. Because the GIDL is proportional to surface potential, GIDL is the function of junction depth in fully depleted shallow junction drain-extension. Therefore, the GIDL is suppressed in a fully depleted shallow junction drain-extension by reducing surface potential. Negative substrate bias and halo doping could suppress the GIDL, too. The GIDL characteristic under negative substrate bias is contrary to other GIDL models.

Thermal stability of ultra-shallow junctions in silicon formed by molecular-beam epitaxy using boron delta doping

Ultra-shallow junction layers are required for deep submicron CMOS and quantum devices. Low-temperature (320 °C) molecular-beam epitaxy was used to form highly conductive, ultra-shallow layers in silicon using boron delta doping. The as-grown junction depths, determined with secondary ion mass spectrometry, ranged from 7 to 18 nm. A minimum resistivity of 3×10 −4 Ω-cm was obtained when the delta-doped layers were spaced 2.5 nm apart. The sheet resistances of the epitaxial layers, plotted as a function of junction depth, followed the theoretical curve for a box-doped layer having a boron doping concentration equal to the solid solubility limit, 6×10 20 cm −3. Minimal change was detected in either the atomic profiles or the resistivity after a 10 s rapid thermal anneal (RTA) or a 10 min furnace anneal (FA) up to 700 °C. The sheet resistance of the as-grown shallow junction are substantially less than that obtained by ion implantation. Only after the 800 °C FA did the MBE-grown layers degrade to have as large a sheet resistance as the best ion implanted layers.

Ultrashallow junctions in silicon formed by molecular-beam epitaxy using boron delta doping

Low-temperature molecular-beam epitaxy was used to form highly conductive, ultrashallow layers in silicon using boron delta doping. Junction depths, determined with secondary ion mass spectrometry, ranged from 7 to 18 nm. A minimum resistivity of 3×10−4 Ω cm was obtained when the delta-doped layers were spaced 2.5 nm apart. The sheet resistances of the epitaxial layers, plotted as a function of junction depth, followed the theoretical curve for a box-doped layer having a boron doping concentration equal to the solid solubility limit, 6×1020/cm3. At a specific thickness, the minimum sheet resistance obtained by B delta doping was more than a factor of 5 less than that achieved by ion implantation.

Study of lateral non-uniformity as a function of junction depth in ultra-shallow junctions and its effect on leakage behavior in as-deposited polycrystalline Si and amorphous Si diodes

Heavily implanted polycrystalline Si films are finding increasing applications as solid diffusion sources, for example, in the formation of ultra-shallow junctions in elevated source/drain metal-oxide-semiconductor field effect transistors and polycrystalline Si emitter bipolar junction transistors. For these applications the dopants are implanted into the polycrystalline Si layer and subsequently diffused into the underlying Si substrate. The diffusion behavior, is however, determined by the evolution of the polycrystalline Si grain microstructure, A large final grain size could lead to laterally more non-uniform and hence leakier junctions. These non-uniformities are lesser for high thermal budget anneals (1100–1150°C, 30 s) than for lower thermal budget anneals (950°C, 30 s) because any doping inhomogeneities in the Si substrate get smeared out as the junction becomes deeper. The junction depth, however, cannot be increased indefinitely from a device viewpoint and a trade-off between leakage current and junction depth has to be made. In this paper, we will study the effect of grain microstructure of ion-implanted as-deposited amorphous Si and as-deposited polycrystalline Si diffusion sources on the diffusion of As and B in the Si substrate, correlate it to the electrical properties of the ultra-shallow junctions formed using this technique.

Electron-beam-induced currents collected by a p-n junction of finite junction depth

The hole-electron pair generation region in a semiconductor bombarded by a scanning electron beam can be modeled as a circular cylinder tangent to the semiconductor surface. A cross-sectional plane normal to the cylinder is then examined. Under conditions of high semiconductor surface recombination velocity, a conformal transformation of this plane can be made to yield a geometry in which the method of images can be used to match boundary conditions at the junction and at the semiconductor surface. Thus, a solution for the electron-beam-induced current (EBIC) problem can be found in this manner when the generation region is external to the diffused or implanted region of a finite junction depth. An infinite series of images can be used to solve the problem when the generation region is within the diffused or implanted region under conditions of low, as well as high, surface recombination velocity. Thus, expected EBIC results are presented as a function of junction depth.

Analytical solutions for avalanche-breakdown voltages of single-diffused gaussian junctions

Closed-form solutions of the potential difference between the 2 edges of the depletion layer of a single diffused Gaussian p- n junction are obtained by integrating Poisson's equation and equating the magnitudes of the positive and negative charges in the depletion layer. By using the closed form solution of the static Poisson's equation and Fulop's average ionization coefficient, the ionization integral in the depletion layer is computed, which yields the correct values of avalanche breakdown voltage, depletion layer thickness at breakdown, and the peak electric field as a function of junction depth. Newton's method is used for rapid convergence. A flowchart to perform the calculations with a programmable hand-held calculator, such as the TI-59, is shown.

The potential of np GaAs solar cells for high efficiency concentrator applications

This communication considers the design of the front grid contact of np GaAs solar cells for high efficiency concentrator applications. This design involves shadowing, contact resistance, and active layer sheet resistance losses, and at high concentrations, the power loss due to voltage drop on the resistance of the grid fingers should be considered. Analysis of the performance can be calculated as a function of junction depth and surface recombination velocity. The junction depth can be optimized by considering its effect on the collection efficiency of the dark current-voltage characteristics or the open circuit voltage, and on the series resistance loss or the fill factor for material parameters. The choice of the material parameters, calculation of the short circuit current, the selection of the n layer thickness, and the cell maximum power and efficiency are discussed. It is concluded that optimized multi-grid structures should allow the use of 10 by 10 sq cm cells with good efficiencies at high concentration ratios, and efficiencies of 22 to 25% should be obtainable from large area cells at concentrations of 40 AM1.

Detection of ultraviolet radiation using silicon carbide p-n junctions

Silicon carbide p- n junctions have been used for the detection of ultraviolet radiation at high temperatures. The wavelength at which the peak response occurred is dependent on the junction depth. Peak response near 2850 Å requires the junction to be < 1- μ deep. The wavelength at peak response increases and the photovoltage decreases with increasing temperature. A number of detectors show response (1–100 mV) at 800°K. The peak wavelength as a function of junction depth may be quantitatively explained by considering the wavelength dependence of the absorption coefficient in silicon carbide below the band edge.

Calculations of cutoff frequency, breakdown voltage, and capacitance for diffused junctions in thin epitaxial silicon layers

Recent developments in high-quality silicon varactors for low-noise parametric amplifiers and high-efficiency harmonic generators necessitate the use of epitaxial silicon layers that are thinner than 10 microns, with resistivity less than 1 Ω-cm. This paper extends Breitschwerdt's recent calculations [1] to such thin epitaxial layers, and also includes the calculation of series resistance and capacitance per unit area in a range useful for microwave diode design. A planar geometry for the junction has been assumed. The impurity distribution of the in-diffusion from the surface and the out-diffusion from the substrate are assumed to be complementary error functions. Depletion layer characteristics of the p-n junction-- including junction depth, impurity gradient at the junction, depletion layer width, capacitance per unit area, and avalanche breakdown voltage--are predicted for various epitaxial layer resistivities. The capacitance per unit area at breakdown is also presented in graphical form. Series resistance has been obtained by numerical integration of various impurity distributions. Zero-bias cutoff frequency for various layer thicknesses is presented graphically as a function of junction depth and breakdown voltage. The calculations predict that there are optimum diffusion conditions for maximum cutoff frequency and for maximum breakdown voltage with a given epitaxial layer thickness. They indicate that the optimum zero-bias cutoff frequency is nearly inversely proportional to the thickness of the epitaxial layer. For instance, the maximum cutoff frequency of a junction in a 2-µ layer can exceed 600 GHz compared with 300 GHz in a 4-µ layer, and 140 GHz in an 8-µ layer. Calculated and experimentally determined characteristics show reasonably good agreement.