|
中原大學九十三學年度碩士班入學招生考試
|
| 93年3月27日 14:00~15:30 電子系固態組 | 誠實是我們珍視的美德， 我們喜愛「拒絕作弊，堅守正直」的你！ |
| 科目：半導體基礎概論 |
| 1. | What crystal growth technique(s) would you employ if you were asked to grow the following: | |
| (a) | a very pure layer of GaAs 20
thick (4%) |
|
| (b) | a GaAs/AlGaAs heterostructure, where each layer is 0.2 thick
(4%) |
|
| (c) | a 50-period multiquantum well in which the well and barrier regions are each 20 monolayers thick (4%) | |
| 2. | Electrons in a semiconductor are affected by two scattering
mechanisms: impurity scattering with the momentum relaxation time of 
s, and lattice scattering with the momentum relaxation time of 2 *
s. |
|
| (a) | What is the total effective momentum relaxation time? (4%) | |
| (b) | If the effective mass is 
where 
is the free electron mass, what is the low field mobility for this semiconductor?
(4%) |
|
| (c) | What is the electron diffusion coefficient for this semiconductor at 77 K? (4%) | |
| (d) | What is the electron thermal velocity for this semiconductor at 77 K? (4%) | |
| 3. | A hypothetical energy band can be fitted approximately to the expression | |
 |
||
| where a is the lattice constant of the crystal. Calculate | ||
| (a) | The effective mass at k=0 (4%) | |
| (b) | The value of k for maximum electron velocity (4%) | |
| (c) | The effective mass at the edge of the Brillouin zone (4%) | |
| 4. | (a) | What is the Fermi energy level? In a semiconductor the Fermi level is 40 meV below the edge of the conduction band and the bandgap is 1.3 eV. What would you do to bring the Fermi level to mid-bandgap? Will the resistivity of the semiconductor change? If so, how? (10%) |
| (b) | An n-type direct bandgap semiconductor has Eg = 1.43 eV at 300°K. It has a shallow donor level with a binding energy of 15 meV and a deep trap level at an energy of 600 meV from the condition band-edge. Draw the E-k diagram showing the conduction and valence bands and the donor and trap levels. [Hint: remember the uncertainty principle.] (10%) | |
| 5. | A semiconductor is doped as a
step junction shown in Fig.1, where  .
Draw the energy band diagram of such a junction and indicate Vbion
this diagram. Also draw the charge density and electric field profile for
such a junction. (20%) |
|
 |
||
| 6. | (a) | Which diode is more suitable for high frequency applications-a Si p-n diode, a Si Schottky diode, or a GaAs Schottky diode? Why? (10%) |
| (b) | Use a simple material structure to explain the mechanism of HEMT (high electron mobility transistor). (10%) | |
|
~ End ~
|
||