Some reasons for nonsaturation of reverse current in junction diodes

The saturation of reverse current for reverse voltages more than a few tenths of a volt, which is predicted for semiconductor junctions by the simple theory, actually never occurs. Effects such as surface conduction and generation of minority carriers in the space-charge region have been used to explain the failure of the current to saturate. The present discussion considers some other possibilities. For nonplanar junctions, increase in the effective junction area with increasing reverse bias may be important. For any junction, increasing bias may move the effective junction surface to places where the semiconductor has, either actually or effectively, different properties. Some examples of these possibilities, chosen to be as closely related to practical devices as possible, are given.     

Elimination or minimisation of optoelectronic crosstalk betweenphotodiodes and electronic devices in OEIC on Si

The optoelectronic crosstalk between photodiodes and electronic devices is observed and investigated in OEICs based on silicon. Results show that the phenomenon is closely related to the diffusion of minority carriers, generated by photon absorption. The crosstalk can be eliminated or minimised by either placing the electronic devices far from the photodiode, or by enclosing them with a reverse-biased guard ring diode     

Computer calculations of avalanche-induced relaxation oscillations in silicon diodes

A digital computer program has been employed to study relaxation oscillations of a silicon p-i-n junction diode reverse-biased into avalanche. The computed plots of diode current and voltage versus time and of diode current versus diode voltage are in good agreement with those obtained experimentally by Hoefflinger. The electric field and charge density distributions across the junction are given for selected times during the breakdown and current decay phases of the oscillations. The electric field is characterized by the formation of a saddle during the avalanche buildup. The variations of power output, efficiency, frequency, and average diode voltage are presented as a function of average current for one particular set of diode and circuit parameters.     

New approach to the design and the fabrication of THz Schottkybarrier diodes

GaAs Schottky barrier diodes with near-ideal electrical and noise characteristics for mixing applications in the terahertz frequency range are described. The conventional formulas describing these characteristics are valid only in a limited forward bias range, corresponding to currents much smaller than the operating currents under submillimeter mixing conditions. Therefore, generalized analytical expressions for the I-V and C-V characteristics of the metal-semiconductor junction in the full bias range are given. A new numerical diode model is presented which takes into account not only the phenomena occurring at the junction, such as current dependent recombination and drift/diffusion velocities, but also the variations of electron mobility and electron temperature in the undepleted epi-layer. A diode fabrication process based on the electrolytic pulse etching of GaAs in combination with an in situ platinum plating for the formation of the Schottky contacts is described. Schottky barrier diodes with a diameter of 1 μm fabricated by this process have already shown excellent results in a 650-GHz waveguide mixer at room temperature     

Charge pumping in SOS—MOS transistors

The variation of the floating-substrate potential of SOS-MOS transistors is studied by applying frequent pulses to the gate. The minority carriers are injected into the floating substrate by charge pumping and they recombine there. The injected charges are stored because of the reverse-biased junctions at the source and drain. The threshold-voltage change by the substrate bias is also investigated. If the silicon film is fully depleted under the gate, the threshold-voltage change does not occur. This condition is used to stabilize the high-speed operations of the SOS-MOS integrated circuits. A new memory cell consisting of only one transistor without a storage capacitor is realized utilizing the change of the floating-substrate potential by the charge pumping and the avalanche multiplication. The sensitivity of the memory cell is affected by the channel length of an SOS-MOS transistor. The memory storage time is obtained as 300 µs.     

从多子角度阐述p-n结理论

传统方法在分析p-n结理论时仅仅关注了过剩少子的扩散电流,但是随着其浓度梯度的降低,扩散电流趋于零,则电流的连续性将难以理解。另外,如果仅仅考虑过剩少子的注入,则无法理解"中性区"的电中性(即电中性条件将被破坏)。针对以上矛盾,以基本的器件物理为基础,分析并得到过剩多子必然存在于中性区,且其分布和数量与过剩少子相同,因而过剩多子的扩散电流也参与p-n结的电流输运。在充分考虑过剩多子的基础上,对p-n结的工作机理可以有更好、更深刻的理解。理想二极管方程在一些假设下仅仅考虑了空间电荷区两边过剩少子的扩散电流,提供了一个很巧妙地计算总电流的方法。     

Impedance and switching of GaAs p-i-n diodes

The impedance of GaAs p-i-n diodes under forward bias is modeled using the two-dimensional simulation program PISCES. A parallel equivalent circuit gives almost constant resistance and capacitance over a wide range of frequencies. The intrinsic turn-off switching time of the diode, neglecting contact resistance, is determined by the sweep out time of the carriers, not by the carrier lifetime, unless this is very short. The diode current is recombination dominated at low forward bias. At higher applied voltages, this current becomes diffusion dominated if not masked by high injection conditions     

Surface effects in sem measurements of hole diffusion length in n-GaAs

In scanning-electron microscope injection measurements of hole diffusion lengths in n-type gallium arsenide Schottky barrier junctions the results obtained depend strongly on the surface treatment (exposure to air, H₂0, or HC1 treatments) after cleaving. The effect is attributed to band bending causing a p-region on the surface which allows collection of minority carriers produced far from the junction. Scanning of the semiconductor surface by the 25 keV electron beam for a few minutes prior to diffusion length measurements is found to remove these contamination effects and give reliable and consistent results.     

AC-driven,color- and brightness-tunable organic light-emitting diodes constructed from an electron only device

In this paper, a color- and brightness-tunable organic light-emitting diode (OLED) is reported. This OLED was realized by inserting a charge generation layer into an electron only device to form an n-i-p-i-n structure. It is shown that, by changing the polarity of applied voltage, only the p-i-n junction operated under positive bias can emit light and, by applying an AC voltage, emission from both junctions was realized. It is also shown that, by using a combination of blue- and red-emiting layers in two p-i-n junctions, both the color and brightness of the resulting white OLED can be tuned independently by changing the positive and negative amplitudes of the AC voltage.     

Switching response of graded-base PN junction diodes

This paper extends the earlier analysis by Kingston of the switching response of a uniform-base diode to a graded-base diode. It concerns the time required to switch a diode from a forward-biased to a reverse-biased condition. The current transient can be separated into two phases: 1) the constant current phase during which the carrier density at the junction changes gradually from a forward-biased to a reverse-biased condition, and 2) the nonconstant current phase during which the injected carriers stored in the base region gradually disappear. In the present analysis, it is found that in a graded-base diode where the impurity concentration decreases from the emitter junction towards the base contact, the time for the constant current phase is greatly shortened because of favorable initial carrier distribution. The effect is already significant if the impurity concentration changes by a factor from 3 to 1 from the emitter junction to the base contact. To shorten the nonconstant current phase, however, a much larger change of impurity concentration, say of the order from 500 to 1, from the emitter junction to the base contact is needed.     

4H-SiC p-i-n紫外光电探测器的电容-电压特性研究

分析并比较了4H-SiC p-i-n紫外光电探测器的电容-电压（C-V）特性随温度和偏置电压的变化情况,观测到4H-SiC p-i-n结构中的深能级缺陷。结果表明：由于近零偏压时探测器i型层已处于耗尽状态,其高频（1 MHz）C-V特性几乎不随反向偏压变化,随着温度升高,被热离化的自由载流子数量增多导致高频结电容随之增大;探测器的低频（100 kHz）结电容比高频结电容具有更强的电压和温度依赖性,原因在于被深能级缺陷俘获的载流子随反向偏压增大或随温度升高而被离化,从而对结电容产生影响。     

Study and modeling of the transport mechanism in a Schottky diode on the basis of a GaAs semiinsulator

The current through a metal-semiconductor junction is mainly due to the majority carriers.Three distinctly different mechanisms exist in a Schottky diode:diffusion of the semiconductor carriers in metal,thermionic emission-diffusion（TED） of carriers through a Schottky gate,and a mechanical quantum that pierces a tunnel through the gate.The system was solved by using a coupled Poisson-Boltzmann algorithm.Schottky BH is defined as the difference in energy between the Fermi level and the metal band carrier majority of the metal-semiconductor junction to the semiconductor contacts.The insulating layer converts the MS device in an MIS device and has a strong influence on its current-voltage（I-V） and the parameters of a Schottky barrier from 3.7 to 15 eV.There are several possible reasons for the error that causes a deviation of the ideal behaviour of Schottky diodes with and without an interfacial insulator layer.These include the particular distribution of interface states,the series resistance, bias voltage and temperature.The GaAs and its large concentration values of trap centers will participate in an increase in the process of thermionic electrons and holes,which will in turn act on the I-V characteristic of the diode,and an overflow maximum value[NT = 3×10²⁰]is obtained.The I-V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.     

Study and modeling of the transport mechanism in a Schottky diode on the basis of a GaAs semiinsulator

The current through a metal-semiconductor junction is mainly due to the majority carriers. Three distinctly different mechanisms exist in a Schottky diode: diffusion of the semiconductor carriers in metal, thermionic emission-diffusion (TED) of carriers through a Schottky gate, and a mechanical quantum that pierces a tunnel through the gate. The system was solved by using a coupled Poisson-Boltzmann algorithm. Schottky BH is defined as the difference in energy between the Fermi level and the metal band carrier majority of the metal-semiconductor junction to the semiconductor contacts. The insulating layer converts the MS device in an MIS device and has a strong influence on its current-voltage (I-V) and the parameters of a Schottky barrier from 3.7 to 15 eV. There are several possible reasons for the error that causes a deviation of the ideal behaviour of Schottky diodes with and without an interfacial insulator layer. These include the particular distribution of interface states, the series resistance, bias voltage and temperature. The GaAs and its large concentration values of trap centers will participate in an increase in the process of thermionic electrons and holes, which will in turn act on the I-V characteristic of the diode, and an overflow maximum value [NT = 3 × 10²⁰] is obtained. The I-V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.     

Response of a P-N junction to a linearly decreasing current

A study is made to determine analytically the time variation of the terminal voltage of a p-n junction in response to a terminal current which starts with a large forward value and continues to decrease linearly until the reverse saturation is attained. It is shown that the period between the reversal of current and the reversal of voltage depends exclusively on the lifetime, diffusion length, and thermal equilibrium densities of minority carriers in both regions of the junction. For some cases, the period between the reversal of current and voltage reduces to half the lifetime of either of the two types of minority carriers. This property allows measuring the lifetime of minority carriers for certain p-n junctions by relatively simple means.     

Visible Light Emission by a Reverse-Biased Integrated Silicon Diode

In this paper, we discuss the emission of visible light by a monolithically integrated silicon diode under reverse bias. The emission of light is achieved using a special defect-engineered buried layer. The light is emitted as punctiform sources by the defects located at the p-n junction of the reverse-biased diode. The influence of the defects on the electrical behavior is manifested as a current-dependent electroluminescence.      

Diffusion length measurements in p-HgCdTe using laser beam induced current

The minority carrier diffusion length in p-HgCdTe is a key indicator of material quality and gives an indication of n-on-p diode performance when the zero bias resistance is diffusion limited. We present results of a temperature dependent study of diffusion length in p-HgCdTe using laser beam induced current (LBIC). Carriers are collected by a p-n junction formed using standard diode junction formation conditions, and thus not necessarily extending to the substrate. Two-dimensional modeling is used to examine the validity of results obtained using this geometry, as compared to the more standard diffusion length test structure geometries, which are harder to fabricate. The temperature dependence of the diffusion length can be compared with theoretical models to determine the dominant recombination mechanisms.     

Excess gate current analysis of junction gate FET's by two- dimensional computer simulation

Gate current in a JFET under high drain bias is much higher than expected from the classical theory for reverse-biased p-n junctions. This excess gate current is caused by minority carriers generated by low-level impact ionization in the conducting channel, while the so-called breakdown voltage is determined by high-level avalanche multiplication near the gate edge at the surface. A simple one-dimensional model for the excess gate current is proposed. This model is based on the results of two-dimensional numerical analysis, which neglects the minority carrier motion. The excess gate current and avalanche breakdown voltage are calculated from one-dimensional ionization integrals, which are obtained numerically by utilizing the solution of two-dimensional analysis. The reverberant effect of the generated carriers on the potential distribution is assumed to be negligible. The results of the calculation are in good agreement with experimental results, without any adjustable parameters. Moreover, various impurity doping profiles are analyzed for the purpose of minimizing excess gate current. The present model requires a reasonably short computation time and is useful for designing JFET devices.     

Evaluation of voltage dependent series resistance of epitaxial varactor diodes at microwave frequencies

The series resistance of a high-quality varactor diode is primarily determined by the resistance of the semiconductor material close to the junction. With increasing reverse bias, the width of the space-charge region becomes greater, and the series resistance decreases. Theoretical models of graded and step junctions have been assumed, and calculations have been made of the series resistance as a function of bias. Epitaxial silicon diodes have been measured for series resistance as a function of bias by using the transmission loss method at 6 to 12 Gc/s, with the diode mounted across a reduced-height waveguide. The variation of series resistance with bias agrees well with the theoretical calculations. By measuring of the 3-dB bandwidth of the series resonance of the diode mounted in the reduced-height waveguide, the junction capacitance and the effective series inductance of the package also can be determined. Because the width of the space-charge region must vary with applied voltage in order to obtain the varactor characteristic, the diode cannot have zero-series resistance at zero-volt bias. The minimum possible series resistance is a function of the breakdown voltage and increases with increasing breakdown voltage. Calculations of the maximum possible cutoff frequency as a function of the diode breakdown voltage are presented for both graded and step junction silicon varactors. A plot of series resistance vs. reverse bias can be used to determine the impurity concentration profile in the epitaxial film. The impurity concentration profile can also be determined by measuring the capacitance vs. reverse bias, a technique which has been in use for some time. However the former method appears to be more accurate in that it is independent of junction area.     

Minority carrier effects upon the small signal and steady-state properties of Schottky diodes

Schottky diode theory is re-evaluated by applying the combined thermionic emission-diffusion theory to both the majority and minority carrier flows across the metal-semiconductor contact. Under both steady-state d.c. and small signal a.c. conditions, numerical solutions to the semiconductor transport equations subject to boundary conditions determined from the combined theory are used to investigate the effects of minority carriers upon the properties of uniformly doped Schottky diodes. High injection effects and contact limitations are shown to influence the minority carrier injection ratio and the total stored minority carrier charge. It is further shown that the small signal impedance of a large class of Schottky diodes becomes inductive under moderate forward bias.     

Operating principles and performance of a novel a-Si:H p-i-n-based X-ray detector for medical image applications

This work develops a novel hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode-based X-ray detector aimed at medical image applications. The new detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, deposited on the p-layer (n-i-p-SiN/sub x/) or the n-layer (p-i-n-SiN/sub x/) of the p-i-n photodiode, as the main charge storage element. This detector operates as a capacitor and is connected in parallel to a reverse-biased p-i-n photodiode during the detection cycle to accumulate photon-converted charges. The junction capacitance (C/sub j/) of the p-i-n diode was enhanced by this stacked dielectric layer without reducing the active area of the detector. The design of the charge storage capacity and the photon-charge transfer efficiency can be optimized separately for various applications. Moreover, the linearity, dynamic range of operation, and data retention capacity of the detector were found to be markedly improved by the enlarged capacitance in the detector. The operating principles and performance of this novel device are discussed, and the corresponding control sequence of the switch of the device array is also addressed. The experimental results proved that this novel structure is valid and can be applied to construct effectively a two-dimensional detection array, offering considerable advantages of the novel device in X-ray medical image applications.