View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Nuclear Engineering and Technology 48 (2016) 1219e1229 Available online at ScienceDirect Nuclear Engineering and Technology journal homepage: www.elsevier.com/locate/net Original Article Computer Modeling, Characterization, and Applications of Gallium Arsenide Gunn Diodes in Radiation Environments * Wafaa Abd El-Basit a, , Safaa Mohamed El-Ghanam a, Ashraf Mosleh Abdel-Maksood b, Sanaa Abd El-Tawab Kamh a, and Fouad Abd El-Moniem Saad Soliman b a Electronics Research Laboratory, Physics Department, Faculty of Women for Arts, Science and Education, Ain-Shams University, Heliopolis, Cairo, Egypt b Nuclear Materials Authority, P.O. Box 530, Maadi, 11728, Cairo, Egypt article info abstract Article history: The present paper reports on a trial to shed further light on the characterization, appli- Received 25 January 2016 cations, and operation of radar speed guns or Gunn diodes on different radiation envi- Received in revised form ronments of neutron or g fields. To this end, theoretical and experimental investigations of 30 March 2016 microwave oscillating system for outer-space applications were carried out. Radiation ef- Accepted 19 April 2016 fects on the transient parameters and electrical properties of the proposed devices have Available online 24 May 2016 been studied in detail with the application of computer programming. Also, the oscillation parameters, power characteristics, and bias current were plotted under the influence of Keywords: different g and neutron irradiation levels. Finally, shelf or oven annealing processes were Domain Excess Field shown to be satisfactory techniques to recover the initial characteristics of the irradiated Gamma Dose devices. Microwave Oscillator Copyright © 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society. This Mobility is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ Neutron Fluence licenses/by-nc-nd/4.0/). Shelf Annealing Transferred Electron Devices 1. Introduction type of semiconductor, on the design of the device and on the operating conditions. Accordingly, the radiation stability The electrical properties of semiconductor devices are of diodes is sometimes determined by the degree of defor- greatly influenced by irradiation, i.e., both the forward- and mation of the forward (IeV) characteristics and sometimes reverse-electrical (IeV) characteristic curves are changed. by the changes in reverse characteristics [1e5]. Transferred However, the magnitude of those changes depends on the electron devices (TEDs), sometimes called Gunn diodes, * Corresponding author. E-mail address: [email protected] (W. Abd El-Basit). http://dx.doi.org/10.1016/j.net.2016.04.009 1738-5733/Copyright © 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1220 Nuclear Engineering and Technology 48 (2016) 1219e1229 (A) 3.00E+015 Neutron fluence, n/cm Initial 9.0x10 5.0x10 2.00E+015 1.2x10 1.00E+015 Average velocity, (m/s) 0.00E+000 02468101214 Applied electric field, (kV/cm) (B) (C) Data 4.0 2.80E+015 Data Linear fit Exponential fit 2.60E+015 3.6 2.40E+015 2.20E+015 3.2 2.00E+015 Applied field, (kV/cm) 1.80E+015 2.8 /s) (m velocity, Average 1.60E+015 2.4 1.40E+015 1E9 1E10 1E11 1E12 1E13 1E14 1E15 1E12 1E13 1E14 Neutron fluence, (n/cm ) Neutron fluence, (n/cm 2) Fig. 1 e Average velocities. Calculated average velocity as a function of (A) applied electric field and (B) applied field. (C) Average velocity as a function of neutron fluence. have been a topic for active research since 1965 [6,7].The 2. Materials and methods Gunn diode is a unique component. Even though it is called a diode, it does not contain a positiveenegative diode 2.1. Computer modeling junction. The Gunn diode can be termed a diode because it has two electrodes. It depends upon the bulk material To study the radiation effects on the output characteristics of properties rather than that of a positiveenegative junction. the transferred electron device, a computer model has been The Gunn diode operation depends on the fact that it has a developed (by the authors) in order to solve the transient voltage-controlled negative resistance [8]. A possible appli- characteristics of the diode such as charge carrier mobility, cation of these diodes involves satellites and military com- domain excess potential, and the outside domain electric munications where radiation tolerance is desired. Damage field. In addition, the waveforms of current density value as a in GaAs devices results from the displacement of lattice function of time for the oscillating diode were obtained under atoms and their subsequent migration and trapping to form the influence of different neutron fluence (4) levels. All the stable and metastable defects. These defects lead to a pro- analyses of the domain behavior of GaAs devices are based on nounced change in both the static and dynamic character- its velocityefield (y-E) characteristics [8e13]. Among them, the istics, but not necessarily in the same way. In addition, Thim [8] model was chosen to be used for this study, where: different defects may arise from various radiation types, h i h i À1 flux rates, and energies. ¼ ð Þ¼ $ þ $ð = Þ4 $ þð = Þ4 y y E m1 E yV E Eo 1 E Eo (1) The principal effect of high energy neutrons on GaAs is to produce defect clusters, which act as trapping where y:velocity;m1: measure of how quickly an electron can 2 and scattering centers for free carriers. In turn, the move through a metal or semiconductor; ¼ 8,000 cm /V.s; E: ¼ effect of these clusters on the device characteristics can applied field in kV/cm; yv: valley velocity and Eo 4.0 kV/cm. be modeled by a carrier removal rate and a fluence- For current calculations, one considers a uniformly doped dependent effective mobility describing the decrease in GaAs diode to which an electric field is applied, which biases it carrier mobility and the reduction in the effective carrier to the negative differential mobility region. Any disturbance in concentration. the field will grow and thus produce a high field domain. In the Nuclear Engineering and Technology 48 (2016) 1219e1229 1221 (A) (B) 7 8,000 ) 6 /cm /V.s) 5 6,000 4 4,000 3 2 Carrier mobility, (cm mobility, Carrier 2,000 Data Data 1 Exponential fit Exponential fit Carrier(x10 concentration, 0 0 1E9 1E10 1E11 1E12 1E13 1E14 1E15 1E8 1E9 1E10 1E11 1E12 1E13 1E14 1E15 Neutron-fluence, (n/cm ) Neutron fluence, (n/cm ) (C) 2.5 ) /cm 2.0 1.5 1.0 0.5 Data Exponential fit Carrier concentration, (x10 Carrier concentration, 0.0 1E9 1E10 1E11 1E12 1E13 1E14 1E15 Neutron fluence, (n/cm ) Fig. 2 e Calculated mobility and concentration. (A) Calculated mobility. Calculated concentration for (B) electrons and (C) holes as a functions of neutron fluence. low field region, the total current will be due to conduction where, mo and no are the preirradiation values of the carrier current and displacement current in this region, while the mobility and carrier concentration, respectively; m and n are field Eo(t) does not vary in the longitudinal direction. This the postirradiation values. implies that the charge density is uniform and equal to the Using these definitions, one can express the neutron- doping charge concentration, Po. Hence, the total current induced carrier removal and mobility changes by: ¼ $ð À $4Þ density J(t) is given by: n no 1 a (6) JðtÞ¼Po$yoðtÞþε$dEoðtÞ=dðtÞ (2) ¼ =ð þ $4Þ m mo 1 b (7) The first term of the above equation represents the con- where the values for the degradation parameters a and b have duction current, where yo(t) is the drift velocity and the second been determined for n-type epitaxially grown GaAs as [8]: ε term represents the displacement current, where is the À Á 2 À4 À0:77 permittivity of GaAs. Finally, the magnitude of the domain a cm ¼ 7:2  10 ðnoÞ (8) potential at any instant (t) can be given as [14]: À Á Zþ∞ 2 À6 À0:64 b cm ¼ 7:8  10 ðnoÞ (9) ð = Þ DVðtÞ¼ DEðx; tÞdx ¼ DVð0Þ$e t td (3) À∞ Fig. 1 shows the average velocity as a function of applied field yeE curve, plotted at different neutron fluence (4) where, DV(0) is the magnitude of the initial disturbance po- values (Fig. 1A), from which the dependence of both the tential which was chosen to be equal to 0.025 V, and td is the applied field (Fig. 1B) and average velocity (Fig. 1C) were decay or growth time of the device. plotted as a function of neutron fluence. It is clear that the 4 The effect of neutron fluence ( ) on the carrier mobility (m) average velocity curves have a negative slope over a broad and effective carrier concentration (n) have been determined range of intermediate field values, which is a necessary e by a number of researchers [15 17]. It is reported that the condition for the existence of negative resistance. Finally, main degradation parameters representing carrier removal empirical equations concerning the obtained data could be rate (a) and mobility (b) are defined as: deduced as: a ¼ð1=noÞ$ðdn=d4Þ (4) E ¼ Ei þ B1$ð4Þ (10) ¼ ð ð = Þ= 4Þ ¼ þ : $ð4Þ b mo d 1 m d (5) E Ei 0 27407 (11) 1222 Nuclear Engineering and Technology 48 (2016) 1219e1229 (b) Carrier concentration (Fig.