Solids I

PREFLIGHT

Please type your (first) name:

Please type your LAST NAME and LAST FOUR SS# digits:

IN:

The following three questions refer to the material you were to read in preparation for the lesson. Questions one and three require you to write a three or four sentence response. Number two is a multiple choice question. Click in the appropriate circle.

You may change your mind as often as you wish. When you are satisfied with your responses, click the SUBMIT button at the bottom of this page. Don't submit more than once. (If you absolutely HAVE to resubmit it, put a note on the end to that effect.)

1. Le Resistance

This NPL simulation is designed to show the effects of various parameters on the resistivity/conductivity of selected semiconductors and an insulator (Diamond).

Controls

The left side of the simulation shows the controls.
The temperature can be varied between 10 and 1000 °K.
There is a choice of three substrates, Silicon, Germanium (semiconductors) and Diamond (insulator).
The two semiconductors can be doped to provide either n type or p type materials by the use of donor impurities or acceptor impurities respectively. There are mulitple choices for each type of impurity, each of which will have an associated ionization energy for the particular substrate it is in. It is also possible to have no impurities and just look at the intrinsic properties of the semiconductor.
The impurity concentration can also be varied, using a logarithmic slider.

Outputs

On the right hand side is shown the outputs from the simulation. The top two bar graphs show the number ratio of majority carriers and resultant resistivity/conductivity using logarithmic scales, a necessity because of the large range of these parameters. The label for the number ratio graph shows the majority carrier (where Ne = number of electrons, Nh = number of holes and Ntot = the total number of valence electrons). To change from a resistivity display to a conductivity display press the button below the bar graph.
The lower figure is a band gap diagram showing the effect of the substrate on the band gap and the effect of adding impurities. The colour of the two bands indicates the number of carriers present in each band using the same colour scale as the graph above. The filled or empty circles represent a logarithmic scale showing the number of electrons/holes that are still to be ionized. When all the circles are full it means that 100% of the donor impurity atoms have electrons. For every circle that becomes empty then this means that the 0.1, 0.01, 0.001 etc. of the donor impurity atoms are ionized. The converse is true for acceptor impurities, i.e. when all the circles are full then all the electron vacancies are filled, this is as if all the holes have ionized.

The mathematical models and data values where derived from "Introduction to Solid State Physics" by C. Kittel and "Introduction to properties of materials" by Rosenthal and Asimow.

By varying the temperature it is very easy to see how the impurity atoms become completely ionized. And by adding impurities it is easy to see the large effect this makes on the resistivity of the material.

At what temperature does pure Silicon conduct electricity as well as cold Silicon doped a very small amount of Phosphorus? Or cold Silicon doped with Indium? Are these temperatures extreme?

2. Impurities

Which of the 7 impurities seems to be fully ionized (most effective) at 10^oK?

Arsenic

Phosphorus

Tin

Indium

3. Chip Making

The device fabrication steps are shown for n-channel Metal-Oxide-Semiconductor (MOS) Field Effect Transistor (FET). All photolithography processes are shown by means of animation. Applet was written for the most part by Mr. Inmook Na, with assistance from Mr. Y. J. Song, under the supervision of C.R. Wie.

How many steps in the manufacture of this transistor require precise alignment? Why is phosphorus used (say instead of indium)? And why is the phosphorus put in at the very beginning instead of waiting until just before the aluminum contacts?

honors extra

Vacuum tubes had 50 years of development before transistors came along. They had all kinds of modifications such as diodes, triodes, tetrodes, pentodes. Tube amplifiers sounded great. And tubes were becoming miniaturized, no bigger than the size of a pencil eraser. So with all this development, why did transistors replace tubes so quickly? What was the advantage to going to silicon?

Below is a space for your thoughts, including general comments about today's assignment (what seemed impossible, what reading didn't make sense, what we should spend class time on, what was "cool", etc.):

You may change your mind as often as you wish. When you are satisfied with your responses, click the SUBMIT button.

I received no help from anyone on this assignment.