Quantum, Solid-state, Plasma and Vacuum The Characteristics of the pin- Structure with a Discrete Metallic Surface i -Region

The Characteristics of the pin -Structure with a Discrete Metallic Surface i -Region Abstract Introduction. The interest in improving pin -structures continues to attract research attention in the field of de-veloping such electronic devices as non-volatile memory, static voltage protection systems, pin -diodes with adjustable characteristics, etc. However, the issue of controlling the characteristics of pin -structures by applying a discrete metallization layer on the surface of the i -region remains to be understudied. Aim. To study the effect of a discrete metallization layer on the i -region surface on the static and dynamic characteristics of the respective pin -structure, the level of defect compensation and the efficiency control of the pin photodetector. Materials and methods. The pin -structure under study comprised a p + -boron-doped region; an n + -phosphorus-doped region; an i -phosphorus-doped region; a semi-insulating substrate; a metallized substrate; a polysilicon control gate; and a silicon oxide dielectric layer. A two-dimensional numerical analysis of the potential distribution, as well as the concentration of free charge carriers and currents, was performed in the Synopsys Sentaurus TCAD environment. Results. A two-dimensional analysis of discretely metallized pin -structures was performed. The stresses applied to the gates of the i -region, which compensated for the influence of defects formed by electron irradiation, were determined. Four pin -photodetector structures were simulated, in which the control gates were realized in the form of a metal–insulator–semiconductor (MIS) structure. The possibility of increasing the sensitivity of pin photodetectors by applying specifically selected potentials to the gates was demonstrated. Conclusion. Effects of a discretely metallized i -region of the pin -structure was studied. A method for correcting the characteristics of the irradiated pin -diode to the initial characteristics was proposed, which permits the use of such diodes in areas with a high radiation level. The design of a high-sensitivity photodetector is proposed, the control gates of which are located on the surface of the i -region. The low-doped i -region is split into two regions ( p - and n –type conductivity). Characteristics of the pin -Structure a Discrete Metallic Surface The Characteristics of the pin -Structure with a Discrete Metallic Surface i -Region The Characteristics of the pin -Structure with a Discrete Metallic Surface i -Region the pin -Structure a i The Characteristics of the pin -Structure with a Discrete Metallic Surface i -Region

Introduction. Pin-diodes with control gates located on the surface of the i-region are increasingly attracting research attention due to their expanded functionality and the ease of integrating with other devices. A number of studies have reported the development of pin-diodes with a discrete metallization layer on the surface of the i-region. Thus, changing the switching time of controlled pin-structures was considered in [1]. Additionally, gate-controlled pindiodes are applicable for the antistatic protection of integrated circuits [2]. Thus, a non-volatile memory device was developed on the basis of a pin-structure in [3]. The integration of controlled pin-structures into non-volatile memory was considered in [4,5]. Recently, the use of 3D shutters in pin-structures has become widespread [6].
Some articles investigated the effect of radiation on instruments and devices. For example, in [7], the degradation of silicon n + -n-p + -structures as a result of exposure to high-energy ( ) 15 16 2 10 10 cm −  electron/proton irradiation was studied. The study [8] aimed to investigate the effect of electron irradiation on the current-voltage curve (CVC) and lowfrequency noise (current and In [9], the CVC and Schottky barrier of a p-type diode were studied depending on the dose of electron irradiation. During irradiation, the crystal structure and electrical properties of semiconductors may vary. In some situations, these parameters are varied intentionally to accurately adjust the speed and capacity of devices. In [10][11][12], the effect of high-energy particle irradiation on the dynamic characteristics of diodes was investigated. It is known that radiation may cause undesirable changes in diode characteristics [13]. A number of studies [14][15][16] were devoted to the effect of metal electrodes located on the surface of the i-region on the properties of respective pin-diodes.
This article is devoted to simulating silicon pindiodes with a discretely metallized surface. The influence of defects, which are associated with electron irradiation of pin-diodes, on the CVC and opening time of such diodes was studied. The static and dynamic characteristics of pin-diodes were corrected by applying specifically selected potentials to the pin-structure gates. The voltages applied to the gates to compensate for the impact of defects were determined.
In addition, the article investigates the influence of metal electrodes located on the surface of the i-region to sensitivity of photodetectors based on pin-structures. Four different designs of pinphotodetectors were studied, the floating gates in which were realized in the form of a metal-insulatorsemiconductor (MIS) structure. The effect of the gate geometry and applied potentials on the sensitivity of the photodetector was elucidated. In addition, the effect of splitting the low-doped i-region into two lowdoped regions of p-and n-type conductivity on the sensitivity of the pin-photodetector was investigated. Simulations were performed in the Synopsys Sentaurus TCAD environment.
Simulation of pin-diodes. The Synopsys Sentaurus TCAD software can be used to describe the traps resulting from irradiation, which create additional energy levels in the band gap, as well as to consider the capture and storage of space charge in the traps. In order to study the effect of electron irradiation on the CVC and opening time of pin-structures, a completely irradiated structure was used. These structures are characterized by a uniform distribution of traps, which have parameters corresponding to those of electron irradiation [17]. For preliminary analysis and modeling, the structure presented in Fig. 1 was selected. During simulations, the geometric dimensions of the control electrodes and their potentials were selected such that the most effective impact on the CVC and switching time could be achieved. Fig. 2 shows the CVC for the initial and electronically irradiated pin-structures across the range from 0 to 1.7 V. In the developed structure with a discretely metallized surface, the contribution of traps to the CVC is compensated by applying voltage to the gates. Positive voltages act similarly to traps, leading to a decrease in the angle of the CVC inclination. Under negative voltages, the opposite situation is observed, thus allowing the impact of defects on the CVC to be compensated. Voltages of different signs applied to the gates produce the best result in terms of correcting the CVC of pin-structures. Thus, when applying a negative voltage to the gate G1 and a positive voltage to the gate G3 , a maximum increase in the slope of the CVC was achieved. An almost linear dependence was reveled between the gate compensating stresses and defect concentrations. Defects in the pin-structure change the rate of the current rise. As a result, a correction of the switching characteristics is required in order to return the opening time to that of a defect-free pin-diode. As shown in [18], the switching characteristics are controlled by the gates on the surface of pin-structures. Fig. 1 shows G1-G3 gates, which provide correction of the switching characteristics given in Fig. 3. The side gates (G1 and G3) provide adjustment of the current and opening time, thus allowing control of the CVC slope and switching characteristics. The introduction of the middle G2 gate into the model allows the opening time to be customized. When a positive bias was applied to G2, the opening time decreased (Fig. 3 , while a negative bias led to an increase in the opening time ( Fig. 3, 3, . The simultaneous use of three gates makes it possible to adjust the switching characteristics of the pin-diode quite accurately, as can be seen when comparing dependencies 1, 2, and 3 in Fig. 3. The correction results are displayed by dependence 5.
Thus, the conducted simulations confirmed the possibility of correcting the characteristics of pinstructures exposed to electron radiation by applying three MIS gates to the diode surface and specifically selected potentials. Adjustable characteristics include the CVC and those of the opening of a pin-structure. The proposed method is suitable for correcting the deviation of the operating characteristics of an irradiated diode to its factory characteristics, thus allowing such diodes to be used in electronics meeting strict requirements for work in high-radiation areas. In addition, the proposed method ensures a longer service life of electronic devices.
Another research aim was to study the effect of metal electrodes (gates) located on the surface of the i-region on the sensitivity of pin-photodetectors. Four designs of pin-photodetectors were studied, in which the control gates were realized in the form of a MIS structure.  The scheme of the initial pin-photodetector is shown in Fig. 4. The effect of the gates located on the surface of the i-region was studied using a photodetector, the structure of which is shown in Fig. 5. The simulation results show that both the gate length in the direction of carrier drift and the potentials at the gates affect the sensitivity of the pinphotodetector rather significantly.
The next stage of the research was to elucidate the effect of splitting the low-doped i-region into two regions -i-p and i-n types -on the sensitivity of the pinphotodetector. Such a design is assumed to contribute to a more efficient separation of electron and hole flows, Gate thickness is 4 nm, gates dielectric thickness is 1.8 nm G1 G2 In the structure shown in Fig. 5, the i-region is formed by doping with phosphorus (i-n). For the separation of charges, a potential of +12 V is applied to both gates. For the separation of charges in the structure in Fig. 6, where the i-region is doped with boron (i-p), a potential of -12 V is applied to both gates. For the separation of charges in the structure in Fig. 7, a potential of -12 V is applied to the gate G1 located on the i-p-region, while the potential +12 V is applied to the gate G2 located on the i-n-region. Voltages at the gates and drain are selected such that the greatest difference between the characteristics of the modified devices and those of the original photodetector could be achieved (see Fig. 4).
In studying the spectral characteristics of pinphotodetectors, a potential of +4 V was applied to the drain. The spectral composition and intensity of optical radiation were assumed to be the same for all topologies. The simulation results shown in Fig. 8 demonstrate that the spectral characteristics of both photodetectors are close, however, the photocurrent (sensitivity to optical radiation) is maximum in the pin-photodetector with full-covering gates and twolayer i-region (Fig. 7). A comparison of the characteristics shows that using of gates leads to a greater separation of electrons and holes in the i-region (Fig. 8, curves 1 and 2). The splitting of the i-region into two layers with different conductivity types, along with extended gates on both sides of the structure (Fig. 7), permits a higher photocurrent to be achieved in comparison with the structure shown in Fig. 6.
The simulations performed in the Synopsys Sentaurus TCAD environment made it possible to study the effect of the Shockley-Read-Hall recombination on the distribution of charge carriers in the i-region of pin-photodetectors. Fig. 9 shows the results obtained for the four investigated structures. When the i-region is divided into two low-doped parts, electrons and holes pass through the semiconductors of the i-n and i-p-conductivity, respectively. In addition, their separation by the vertical field of fullcovering gates (structure according to Характеристики pin-структуры с дискретно металлизированной поверхностью i-области The Characteristics of the pin-Structure with a Discrete Metallic Surface i-Region more efficiently than when the gates are located on one side (structure according to Fig. 6) (Fig. 9, c and  d). As a result, for topologies with a split i-region, the Shockley-Read-Hall recombination manifests itself to a lesser degree: the more efficiently the carriers are separated by the gate field, the less pronounced the Shockley-Read-Hall recombination becomes. Thus, the introduction of layers of different conductivity types in the i-region of pinphotodetectors in combination with full-covering gates on both sides, allows the photocurrent to be increased up to about 20%, compared to basic pinphotodetectors.
Discussion. The article solves the problem of controlling the characteristics of pin-structures using gates on the surface of the i-layer. Such problems are encountered in the development of non-volatile memory, static voltage protection devices, pin-diodes with adjustable characteristics, etc. The proposed method for correcting the characteristics of an irradiated pin-diode to its original characteristics opens up the possibility of using such diodes in electronics meeting strict requirements for work in highradiation areas.
A 2D calculation of the distribution of the concentration of free charge carriers and potential in the pin-structure of a photodetector was carried out. A structure for a high-sensitivity photodetector featuring control gates on the surface of the i-region and the separation of the low-doped i-region structure into two regions with p-and n-types of conductivity was proposed. The conducted research confirmed that a discrete metallization of the surface of the iregion has a positive effect on the main characteristics of devices based on pin-structures.