bdbarkana@aol.com hherkaya@ogu.edu.tr
Abstract
A model is proposed for the resonant tunneling bipolar transistor current voltage characteristics. The model is based on a model for the resonant tunneling diode and the traditional Ebers-Moll model of the bipolar transistor. A device structure was simulated, and characteristics that resemble that of the resonant tunneling transistor were obtained.
1. Introduction
The first resonant tunneling diode (RTD) was reported by Chang, Tsu and Esaki in 1973 [1]. Since then, detailed studies on resonant tunneling diodes led to the invention of resonant tunneling transistors (RTBT).
Especially in the last ten years, many theoretical and experimental studies have been published in this area (Pan et al, 2001 [2]; Cheng et al, 1999 [3]; Tsai, 2001 [4];
Lacomb and Jain, 1996 [5]; Bigalow and Leburton, 1994 [6]; Taniyama et al, 1994 [7]). In these studies, mostly AlGaAs, GaAs, and InGaAs materials were used, and the common emitter current gain was obtained around 140.
The resonant tunneling devices can be used to design high performance electronic systems owing to their multi-state nature.
In this study, we suggest a simple model for RTBT that is based on the resonant tunneling phenomenon and traditional Ebers-Moll bipolar transistor model. The Ebers-Moll model is used to calculate current and voltage values. The resulting current-voltage characteristic of the RTBT structure is found to be similar to experimental results. Simulation was carried out on Matlab.
2. Structure of the Resonant Tunneling Diode
A resonant tunneling diode is a two-terminal quantum-effect device made of two undoped quantumbarriers and an undoped quantum well. A typical physical structure of the RTD is shown in Figure 1. For the simulation, the doping concentrations of both p- and n-type doped regions are assumed to be 1017 cm-3. Layer widths of barrier regions and well region are assumed as 5 nm and 3 nm, respectively.
The current density through the RTD is given by Nag [8] as
( E ) T T [ f E f E e V ] d k
J e
3 kl u* u( ) ( )
38
2 ⎟ ∇ − +
⎠
⎜ ⎞
⎝
= ⎛ π = ∫
(1)where,
k
l is the wave vector component perpendicular to the junction interface; E, electron energy; Tu, the transmission probability; V, applied voltage;d
3k
, the volume element in the wave vector;f (E )
, the Fermi electron distribution function. The current-voltage characteristic of the RTD, which is obtained through the simulation, is shown in Figure 2.p+ GaAs
Undoped Al0.3Ga0.7As Undoped GaAs Undoped Al0.3Ga0.7As n GaAs
n+ GaAs
Figure 1. The structure of the resonant tunneling diode.
T. Sobh et al. (eds.), Innovative Algorithms and Techniques in Automation, Industrial Electronics and Telecommunications, 75–78.
© 2007 Springer.
75
Figure 2. Current-voltage characteristic of the RTD.
3. A Model for the Resonant Tunneling Bipolar Transistor
In this section, a simple RTBT is proposed which is based on Ebers-Moll model. The model is given in Figure 3.
Figure 3. A circuit model for the Resonant Tunneling Bipolar Transistor
The base and collector currents of the RTBT are the same as that of the base and collector current of the heterojunction bipolar transistor (HBT). The current and voltage equations of RTBT can be expressed as follows:
RTD HBT
The first step to find RTBT’s current-voltage characteristic is to calculate the current,
I
RTD, of the RTD for a given voltage,V
RTD. Here,I
RTD is also equal to the emitter current of the RTBT. Therefore, base-emitter voltage of the HBT can be found using Ebers-Moll model for the givenI
RTD. This voltage value,V
BEHBT, isCollector and base currents can be calculated using the voltage value,
V
BEHBT: current gains that are calculated for the BJT structure for the given bias conditions.The physical properties of the RTBT in this study are assumed as shown in Figure 4. A similar structure was used experimentally by Wu et al in 1991 [9].
BARKANA AND ERKAYA 76
Figure 4. The physical structure of the RTBT.
4. Results
The simulation results for the current-voltage characteristics of the RTBT based on the model presented above are given Figure 5 and Figure 6. According to the characteristics in Figure 5, the device has the typical characteristics of the resonant tunneling transistor. The characteristics have the negative differential resistance region for the base-emitter voltage range 3.2 V – 4.0 V.
The collector current appears to be constant for a given base-emitter voltage regardless of the base collector voltage as long as the base-collector voltage is kept above 0.5 volts.
Figure 5. The collector and base currents versus base-emitter voltage of the RTBT for
V
CE= 1 . 5
V.Figure 6.
I
C− V
CE Characteristics of the RTBT for variousV
BE5. Conclusion
The model that is consisted of a resonant tunnel diode and a bipolar transistor provides characteristics that resemble the characteristics of the resonant tunneling bipolar transistors.
REFERENCES
[1] L. L. Chang, L. Esaki, and R. Tsu, “Resonant Tunneling in Semiconductor Double Barriers” Appl. Phys.
Lett., vol.24, p. 593, 1974.
[2] H-J. Pan, S.C. Feng, W.C. Wang, K.W. Lin, K.H. Yu, C.Z. Wu, L.W. Laih, and W.C. Liu, “Investigation of an InGaP/GaAs resonant tunelling heterojunction bipolar transistor,” Solid State Electronics, No.45, pp.489-494, 2001.
[3] S.Y. Cheng, J.H. Tsai, W.L. Chang, H.J. Pan, Y.H.
Shie, and W.C. Liu, “Investigation of an InGaP/GaAs resonant tunneling transistor (RTT)”, Solid-State Electronics, Vol.43, pp.755-760, 1999.
[4] J.H. Tsai, “Quantized Resonant Tunneling Phenomena of AlGaAs/InGaAs Heterojunction Bipolar Transistors”, Japanese Journal of Applied Physics, Vol.40, pp. 5865-5870, 2001.
MODEL FOR RESONANT TUNNELING BIPOLAR TRANSISTORS 77
[5] R. Lacomb and F. Jain, “A self-consistant model to simulate large-signal electrical characteristics of resonant tunneling bipolar transistors”, Solid State Electronics, Vol.39, No. 11, pp 1621-1627, 1996.
[6] J.M. Bigelow, J.P. Lepurton, “Self-Consistent Modelling of Resonant Interband Tunneling in Bipolar Tunneling Field-Effect Transistors”, IEEE Transactions on Electron Devices, Vol.41, pp.125-131, 1994.
[7] H.Taniyama, M. Tomizawa, A. Yoshii, “Two-dimensional analysis of resonant tunneling using the
time-dependent Schrodinger equation”, Japanese Journal of Applied Physics, Vol.33, pp.1781-1786, 1994.
[8] B.R Nag, Physics of Quantum Well Devices, Boston:
Kluwer Academic Publishers, Dordrecht, 2000.
[9] J. S. Wu, C. Y. Chang, C.P. Lee, K.H. Chanh, D.G.
Liu, and D.C. Liou, “Characterization of Improved AlGaAs/GaAs Resonant Tunneling Heterostructure Bipolar Transistors”, Japanese Journal of Applied Physics, Vol. 30, No.2A, pp. L160-L162, 1991.
BARKANA AND ERKAYA 78
Abstract— One of the most important requirements in government websites is the security. The Data Protection Act, Human Rights Act and other legislation require that privacy is respected. Beyond this, Government websites must be secure to build trust and maintain the reputation of electronic government.
This will be seriously damaged if websites are defaced, services are unavailable or sensitive information is released to the wrong people. Securing a Web application is difficult, not only because of various technical departments coordination involved, but also because most security tools are not designed to address the Web application as a whole, including how the different pieces of the application interact with each other. The potential for a security breech exists in each layer of a Web application. Traditional security solutions, such as access control or intrusion detection/prevention systems, are specialized to protect different layers of the Internet infrastructure, and are usually not designed to handle HTTP and HTML attacks. While these tools are useful for their specific functions, they do not address all of the issues that Web applications present. More important, using these tools can give administrators a false sense of confidence if they do not know that the other vulnerabilities exist. This paper is being performed in the context of the e-Voto project, a Portuguese project dealing with the complexity of the electronic voting systems, in particular to the dissemination of electoral results over the WWW. So, in this paper the authors present some recommendations to web applications development that manage and present important information like electoral results with medium-high security level.
Index Terms— Vote, Web security, Electroral results, E-Democracy
I. INTRODUCTION
Web application development is very different from other development environments. The Web browsers and the nature of HTTP pose security pitfalls not found in traditional client-server applications.
Carlos Serrão is with Adetti/ISCTE - Ed. ISCTE – Av. das Forças Armadas, 1600-082, Lisboa, Portugal; (e-mail: Carlos.Serrao@iscte.pt , Miguel.Dias@iscte.pt.)
António Pacheco is with Marinha de Guerra Portuguesa, Direcção de Análise e Gestão de Informação, Lisboa, Portugal; (e-mail:
guerreiro.pacheco@marinha.pt).
Web developers must know how web servers and browsers interact, the nature of Internet communications, and the attacks web applications undergo on the Internet.
The technical staff cannot rely on the fact that a Web Server (and/or web-applications) is secured by the usage of a firewall and network intrusion detection system. Security flaws in web applications easily bypass firewalls and other basic security measures. Many banking, military and e-commerce sites have learned that lesson on the hard way. It's easy for a medium-experienced software developer to create a web application that allows outsiders access to files on the server, gather passwords and customer information, and even alter the application itself despite firewalls and other security measures.
This document presents e-Democracy web application security problems. The examples are specific, the flaws and concepts described apply to all languages and platforms: such as .Net, ASP, PHP, Servlets, Cold Fusion and more.
II. E-DEMOCRACY WEB SITES SECURITY AREAS
A. The security of website
It needs to be stressed that most successful breaches of integrity on websites are made possible by misconfiguration of the web server itself and failure to install relevant security patches. The information in this section aims to raise awareness on correct configuration and patch application.
The security of a website is determined by the security of the following [9]:
• the web server application; the operating system of the web server computer;
• the local area network of the web server computer;
• ‘backend’ (eg database) applications supporting the web server;
• the authoritative domain name server for the web server network;
• remote web server administration, eg, use of FTP, use of server extensions (not addressed here), and
• physical and personnel measures in place to ensure that the web server environment is secure, but these are beyond the scope of this guidance.
In the sections below each area of security will be considered sequentially with recommendations for each. All of the recommendations should be followed if good website