ACUTE—Assembly for Computational Electronics
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1  [[Image(picture_11.png, 700px, class=aligncenter)]]  

2  
3  This nanoHUB "topic page" provides an easy access to selected nanoHUB educational material on computational electronics that is openly accessible.  
4  
5  We invite users to participate in this open source, interactive educational initiative:  
6  
7  * [http://www.nanohub.org/contribute/Contribute content] by uploading it to the nanoHUB. (See "Contribute Content") on the nanoHUB mainpage.  
8  * Provide feedback for the items you use on the nanoHUB through the review system. (Please be explicit and provide constructive feedback.)  
9  * Let us know when things do not work by filing a ticket through the nanoHUB "Help" feature on every page.  
10  * Finally, let us know what you are doing and [http://www.nanohub.org/feedback/suggestions/your suggestions] improving the nanoHUB by using the "Feedback" section, which you can find under "[http://www.nanohub.org/support/ Support]"  
11  
12  Thank you for using the nanoHUB, and be sure to [http://www.nanohub.org/feedback/success_story/share your nanoHUB success stories] with us. We like to hear from you, and our sponsors need to know that the nanoHUB is having impact.  
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14  [[Div(start, class=clear)]][[Div(end)]]  
15  
16  The purpose of the ACUTE toolbased curriculum is to introduce interested scientists from academia and industry to the advanced methods of simulation needed for the proper modeling of stateoftheart nanoscale devices. The multiple scale transport in doped semiconductors is summarized in the figure below, in terms of the transport regimes, relative importance of the scattering mechanisms, and possible applications.  
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18    [[Image(intro1.png, 250px, class=align 
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21  ACUTE begins with a discussion of the energy band structure that enters as an input to any device simulator. The next section offers a discussion of simulators that involve the driftdiffusion model, and then simulations that involve hydrodynamic and energybalance transport, and conclude the semiclassical transport modeling with application of particlebased device simulation methods.  
22  
23  After the study and utilization of the semiclassical simulation tools and their applications, the next step includes quantum corrections into the classical simulators. The final set of tools is dedicated to the farfrom equilibrium transport, where the concept of pure and mixed states and the distribution function is introduced. Several tools that utilize different methods will be used for that purpose, such as tools that use the recursive Green’sfunction method and its variant, the Usuki method, as well as the Contact Block Reduction tool, as the most efficient and complete way of solving the quantumtransport problem because this method allows users to simultaneously calculate sourcedrain current and gate leakage (which is not the case, for example, with the Usuki and the recursive Green’s function techniques that are in fact quasi onedimensional in nature for transport through a device). A table that shows the advantages and the limitation of various semiclassical and quantumtransport simulation tools is presented below.  
24  
25  [[Image(intro3.png, 250px, class=alignleft)]]  
26  [[Div(start, class=clear)]][[Div(end)]]  
27  
28  More details on the actual tool design and information on commercial tool usage can be found on the web pages:  
29  
30  [[Resource(4921)]]  
31  
32  [[Resource(5092)]]  
33  
34  
35  == Energy Bands and Effective Masses ==  
36  
37  === [/tools/acute/ Piecewise Constant Potential Barrier Tool in ACUTE]– Open Systems ===  
38  [[Image(pcpbt.png, 200px, class=alignleft)]]  
39  The [/tools/acute/ Piecewise Constant Potential Barrier Tool in ACUTE] allows users to calculate the transmission and the reflection coefficient of arbitrary five, seven, nine, eleven and 2nsegment piecewise constant potential energy profile. For the case of a multiwell structure, it also calculates the quasibound states. Thus the Piecewise Constant Potential Tool can be used as a simple demonstration tool for the formation of energy bands.  
40  
41  Other uses include: 1) in the case of stationary perturbation theory, as an exercise to test the validity of the firstorder and the secondorder correction to the ground state energy of the system due to small perturbations of the confining potential, and 2) as a test of the validity of the Wentzel–Kramers–Brillouin (WKB) approximation for triangular potential barriers.  
42  
43  Exercises:  
44  
45  * [[Resource(4831)]]  
46  
47  * [[Resource(4833)]]  
48  
49  * [[Resource(4853)]]  
50  
51  * [[Resource(4873)]]  
52  
53  * [[Resource(5319)]]  
54  
55  * [[Resource(4849)]]  
56  
57  * [[Resource(5102)]]  
58  
59  * [[Resource(5130)]]  
60  
61  [[Div(start, class=clear)]][[Div(end)]]  
62  
63  === [/tools/acute/ Periodic Potential Lab in ACUTE] ===  
64  [[Image(ppl.png, 250px, class=alignleft)]]  
65  
66  The [/tools/acute/ Periodic Potential Lab in ACUTE] solves the timeindependent Schrödinger Equation in a onedimensional spatial potential variation. Rectangular, triangular, parabolic (harmonic), and Coulomb potential confinements can be considered. The user can determine energetic and spatial details of the potential profiles, compute the allowed and forbidden bands, plot the bands in a compact as well as an expanded zone, and compare the results against a simple effectivemass parabolic band. Transmission is also calculated. This lab also allows students to become familiar with the reducedzone and expandedzone representation of the dispersion relation (i. e. the Ek relation for carriers).  
67  
68  Exercises:  
69  
70  * [[Resource(4851)]]  
71  
72  [[Div(start, class=clear)]][[Div(end)]]  
73  
74  
75  === [/tools/acute/ Band Structure Lab in ACUTE] ===  
76  [[Image(bsl.png, 250px, class=alignleft)]]  
77  
78  In solidstate physics, the electronic band structure (or simply band structure) of a solid describes ranges of energy that an electron is "forbidden" or "allowed" to have. It is due to the diffraction of the quantum mechanical electron waves in the periodic crystal lattice. The band structure of a material determines several characteristics, in particular its electronic and optical properties. The [/tools/acute/ Band Structure Lab in ACUTE] enables the study of bulk dispersion relationships of silicon (Si), gallium arsenide (GaAs), and indium arsenide (InAs). Plotting the full dispersion relation of different materials, students first get familiar with a band structure of direct bandgap (gallium arsenide and indium arsenide) and indirect bandgap semiconductors (silicon). In the case of multiple conduction band valleys, the user has first to determine the Miller indices of one of the equivalent valleys and then from that information it immediately follows, e. g., how many equivalent conduction bands one has in silicon and germanium (Ge).  
79  
80  In advanced applications, the users can apply tensile and compressive strain and observe the variation in the band structure, bandgaps, and effective masses. Advanced users can also study bandstructure effects in ultrascaled (thin body) quantum wells, and nanowires of different cross sections. Band Structure Lab uses the ''sp3s*d5'' tight binding method to compute dispersion (Ek) for bulk, planar, and nanowire semiconductors.  
81  
82  Exercises:  
83  
84  * [[Resource(5201)]]  
85  
86  * [[Resource(5031)]]  
87  
88  * [[Resource(4890)]]  
89  
90  * [[Resource(4880)]]  
91  
92  
93  [[Div(start, class=clear)]][[Div(end)]]  
94  
95  
96  ==DriftDiffusion and Energy Balance Simulations==  
97  
98  
99  === [/tools/acute/ PADRE Tool in ACUTE]—Modeling of siliconbased devices===  
100  [[Image(padre.png, 250px, class=alignleft)]]  
101  
102  [/tools/acute/ PADRE Tool in ACUTE] is a twodimensional/threedimensional simulator for electronic devices, such as MOSFET transistors.  
103  
104  PADRE Tool in ACUTE is a 2D/3D simulator for electronic devices, such as MOSFETs. With PADRE, users can simulate physical structures of arbitrary geometryincluding heterostructureswith arbitrary doping profiles, which can be obtained using analytical functions or directly from such multidimentional process simulators as Prophet  
105  For each electrical bias, [/tools/acute/ PADRE Tool in ACUTE] solves coupled sets of partial differential equations (PDEs). The variety of PDE systems supported in PADRE form a hierarchy of accuracy: 1) electrostatic (Poisson equations), 2) driftdiffusion, including carrier continuity equations, 3) energy balance, including carrier temperature, and 4) electrothermal, including lattice heating.  
106  
107  Listed below are tools, exercises, and sets of problems that utilize the [/tools/acute/ PADRE Tool in ACUTE]:  
108  
109  * [[Resource(229)]]  
110  
111  * [[Resource(4894)]]  
112  
113  * [[Resource(4896)]]  
114  
115  * [[Resource(452)]]  
116  
117  * [[Resource(4906)]]  
118  
119  * [[Resource(3984)]]  
120  
121  * [[Resource(5051)]]  
122  
123  Supplemental documentation:  
124  
125  * [/site/resources/tools/padre/doc/index.html User Manual]  
126  
127  * [/site/resources/2006/06/01581/intro_dd_padre_word.pdf Abbreviated First Time User Guide]  
128  
129  A set of course notes on computational electronics with detailed explanations on band structure, pseudopotentials, numerical issues, and drift diffusion is also available.  
130  
131  * [[Resource(1516)]]  
132  
133  * [[Resource(980)]]  
134  
135  
136  ===SILVACO Simulator—Modeling of SiliconBased and IIIV Devices===  
137  
138  In preparation.  
139  
140  
141  == ParticleBased Simulators ==  
142  
143  === [/tools/acute/ Bulk Monte Carlo Lab in ACUTE] ===  
144  [[Image(scattering.png, 250px class=alignleft)]]  
145  [[Image(mc.png, 250px, class=alignright)]]  
146  
147  The [/tools/acute/ Bulk Monte Carlo Lab in ACUTE] calculates the bulk values of the electron drift velocity, electron average energy, and electron mobility for electric fields applied in arbitrary crystallographic direction in both column 4 (silicon and germanium) and IIIV (gallium arsenide, silicon carbide and gallium nitride) materials. All relevant scattering mechanisms for the materials being considered have been included in the model.  
148  
149  Detailed derivation of the scattering rates for most of the scattering mechanisms included in the model can be found on Prof. Vasileska personal website 

150  
151  [[Resource(4843)]]  
152  
153  An A/V presentation is also available:  
154  
155  [[Resource(4439)]]  
156  
157  that gives more insight on the implementation details of the Ensemble Monte Carlo technique for the solution of the Boltzmann Transport Equation. Examples of simulations that can be performed with this tool are given below:  
158  
159  [[Resource(4845)]]  
160  
161  Exercises:  
162  
163  * [[Resource(5047)]]  
164  
165  * [[Resource(5277)]]  
166  
167  * [[Resource(5275)]]  
168  
169  * [[Resource(5321)]]  
170  
171  * [[Resource(5323)]]  
172  
173  
174  === [/tools/acute/ Quamc2D Lab in ACUTE] ===  
175  [[Image(quamc2d1.png, 250px, class=alignleft)]] [[Image(quamc2d2.png, 250px, class=alignleft)]]  
176  
177  [/tools/acute/ Quamc2D Lab in ACUTE]  
178  
179  QuaMC 2D (pronounced "quamsee") is a quasi threedimensional quantumcorrected semiclassical MonteCarlo transport simulator for conventional and nonconventional MOSFET devices.  
180  
181  A parameterfree quantum field approach has been developed and utilized quite successfully in order to capture the sizequantization effects in nanoscale MOSFETs. The method is based on a perturbation theory around thermodynamic equilibrium and leads to a quantum fieldformalism in which the size of an electron depends upon its energy. This simulator uses different selfconsistent eventbiasing schemes for statistical enhancement in the MonteCarlo device simulations. Enhancement algorithms are especially useful when the device behavior is governed by rare events in the carrier transport process. A bias technique, particularly useful for small devices, is obtained by injection of hot carriers from the boundaries. Regarding the Monte Carlo transport kernel, the explicit inclusion of the longitudinal and transverse masses in the silicon conduction band is realized in the program using the HerringVogt transformation. Intravalley scattering is limited to acoustic phonons. For the intervalley scattering, both g and fphonon processes have been included.  
182  
183  * [[Resource(4520)]]  
184  
185  * [[Resource(4543)]]  
186  
187  * [[Resource(4443)]]  
188  
189  * [[Resource(4439)]]  
190  
191  * [[Resource(5127)]]  
192  
193  Exercises:  
194  
195  ===Thermal ParticleBased Device Simulator===  
196  
197  In preparation.  
198  
199  Exercises and Other Resources:  
200  
201  * [[Resource(5350)]]  
202  
203  
204  ==Inclusion of Quantum Corrections in Semiclassical Simulation Tools==  
205  
206  
207  === [/tools/acute/ Schred in ACUTE] ===  
208  [[Image(schred.png, 250px, class=alignleft)]]  
209  [/tools/acute/ Schred in ACUTE] calculates the envelope wavefunctions and the corresponding boundstate energies in a typical MOS (MetalOxideSemiconductor) or SOS (SemiconductorOxide Semiconductor) structure and a typical SOI structure by solving selfconsistently the onedimensional Poisson and Schrödinger equations.  
210  
211  To better understand the operation of [/tools/acute/ Schred in ACUTE] and the physics of MOS capacitors please refer to:  
212  
213  * [[Resource(4794)]]  
214  
215  * [[Resource(4796)]]  
216  
217  * [[Resource(5087)]]  
218  
219  * [[Resource(5127)]]  
220  
221  Exercises:  
222  
223  * [[Resource(4900)]]  
224  
225  * [[Resource(4902)]]  
226  
227  * [[Resource(4904)]]  
228  
229  
230  === [/tools/acute/ 1D Heterostructure Tool in ACUTE] ===  
231  [[Image(1dhet1.png, 180px, class=alignleft)]] [[Image(1dhet2.png, 180px, class=alignleft)]]  
232  
233  The [/tools/acute/ 1D Heterostructure Tool in ACUTE] simulates the confined states in onedimentional heterostructures by selfconsistently calculating their charge based on a quantummechanical description of the onedimensional device. Increased interest in high electron mobility transistors (HEMTs) is due to the eventual limitations reached by scaling conventional transistors. The 1D Heterostructure Tool in ACUTE is a very valuable tool for the design of HEMTs because the user can determine such components as the position and the magnitude of the deltadoped layer, the thickness of the barrier, and the spacer layer, for which the user can maximize the amount of free carriers in the channel, which, in turn, leads to a larger drive current.  
234  
235  Exercises:  
236  
237  * [[Resource(5231)]]  
238  
239  * [[Resource(5233)]]  
240  
241  
242  The most commonly used semiconductor devices for applications in the GHz range now are gallium arsenide based MESFETs, HEMTs and HBTs. Although MESFETs are the cheapest devices because they can be realized with bulk material, i.e. without epitaxially grown layers, HEMTs and HBTs are promising devices for the near future. The advantage of HEMTs and HBTs compared to MESFETs is a higher power density (by a factor of two to three), which leads to a significantly smaller chip size.  
243  
244  HEMTs are fieldeffect transistors wherein the flow of the current between two ohmic contacts, known as the source and the drain, is controlled by a third contact, the gate. Such gates are usually Schottky contacts. In contrast to ionimplanted MESFETs, HEMTs are based on epitaxial layers with different band gaps.  
245  
246  
247  ==Quantum Transport==  
248  
249  
250  === Recursive Green's Function Method for Modeling RTD's===  
251  
252  in preparation.  
253  
254  
255  === [/tools/acute/ nanoMOS in ACUTE] ===  
256  [[Image(nanomos.png, 250px, class=alignleft)]]  
257  
258  [/tools/acute/ nanoMOS in ACUTE] is a twodimensional simulator for thin body (less than 5 nm), fully depleted, doublegated nMOSFETs. Five transport models is available (driftdiffusion, classical ballistic, energy transport, quantum ballistic, and quantum diffusive). The transport models treat quantum effects in the confinement direction exactly, and the names indicate the technique used to account for carrier transport along the channel. Each of these transport models is solved selfconsistently with Poisson's equation. Several internal quantities such as subband profiles, subband areal electron densities, potential profiles, and currentvoltage (I/V) information can be obtained from the source code.  
259  
260  [[Resource(1305)]] 3.0 includes an improved treatment of carrier scattering. Some important information about [/tools/acute/ nanoMOS in ACUTE] can be found on the following links:  
261  
262  * [[Resource(2845)]]  
263  
264  * [[Resource(1533)]]  
265  
266  
267  ===CBR===  
268  
269  in preparation.  
270  
271  
272  ==Atomistic Modeling==  
273  
274  
275  === [/tools/acute/ NEMO3D in ACUTE] ===  
276  [[Image(modeling_agenda5.gif, 250px, class=alignleft)]] [[Image(qdot.png, 250px, class=alignleft)]]  
277  
278  [/tools/acute/ NEMO3D in ACUTE] calculates eigenstates in (almost) arbitrarily shaped semiconductor structures in the typical column IV and IIIV materials. Atoms are represented by the empirical tight binding model using ''s'', ''sp3s*'', or ''sp3d5s*'' models with or without spin. Strain is computed using the classical valence force field (VFF) with various Keatinglike potentials.  
279  
280  Users of [/tools/acute/ NEMO3D in ACUTE] can analyze quantum dots, alloyed quantum dots, longrange strain effects on quantum dots, the effects of wetting layers, piezoelectric effects in quantum dots, quantumdot nuclearspin interaction, quantumdot phonon spectra, coupled quantumdot systems, miscut silicon quantum wells with silicongermanium alloy buffers, coreshell nanowires, alloyed nanowires, phosphorous impurities in silicon (P:Si qubits), and buck alloys.  
281  
282  Boundary conditions to treat the effects of surface states have been developed. Direct and exchange interactions and interactions with electromagnetic fields can be computed in a postprocessing approach based on the NEMO 3D single particle states.  
283  
284  Exercises:  
285  
286  * [[Resource(450)]]  
287  
288  * [[Resource(2925)]]  
289  
290  == Collection of tools that comprise ACUTE ==  
291  
292  [[Resource(4826)]]  
293  
294  [[Resource(3847)]]  
295  
296  [[Resource(1308)]]  
297  
298  [[Resource(941)]]  
299  
300  [[Resource(4438)]]  
301  
302  [[Resource(1092)]]  
303  
304  [[Resource(221)]]  
305  
306  [[Resource(5203)]]  
307  
308  [[Resource(1305)]]  
309  
310  [[Resource(450)]] 