Reading Materials
Barrier Height and Capacitance
The barrier height can be determined by the capacitance measurement. When a small ac voltage is superimposed upon a dc bias，incremental charges of one sign are induced on the metal surface and charges of the opposite sign in the semiconductor. Fig.9.9 shows some typical results where 1/C2 is plotted against the applied voltage.
Fig.9.9 1/C2 versus applied voltage for W-Si and W-GaAs diodes.
To obtain the barrier height of semiconductor which contain both shallow-level and deep-level impurities，we need to measure the C-Vcurves at two different temperatures at multiple frequencies.
Drawing the Energy Bands
Start with the metal，draw the Fermi level for the semiconductor in the right place allowing for any external voltage，then draw the energy bands for the bulk semiconductor to fit round the Fermi level. Next locate the bottom of the conduction band at the surface by measuring up by Wm from the metal Fermi level，measuring down by Ws and correcting for the gap between conduction band and Fermi level in the semiconductor. This last stage can be more tidily expressed by saying that，at the surface，the bottom of the conduction band is Wm-χs above the metal Fermi level，where χs is the electron affinity of the semiconductor. Finally complete the bent bands in the semiconductor. Their thickness is once again governed by charges in the depletion layer through Poisson’s equation. Notice that since the potential in the semiconductor is now no longer uniform，the carrier density will also vary. The local difference between the band edges and the Fermi level must be used to find hole and electron densities.
Words and Expressions
intimate adj. 亲密的
disparity n. 不一致，不同，不等
infinitesimal adj. 无穷小的，极小的，无限小的
vicinity n. 邻近，附近，接近
remote adj. 遥远的，偏僻的，细微的
curvature n. 弯曲，曲率
impede v. 阻止
Glossary of Important Term
Schottky contacts 肖特基接触
ohmic contacts 欧姆接触
work function 功函数
electron affinity 亲和势
depletion approximation 耗尽近似
tunneling 隧穿
Exercises
1. Translate the first paragraph in the reading material into Chinese.
2. Answer the following questions in English.
（1）Describe the charge flow in a forward-biased Schottky barrier diode.
（2）Describe what is meant by an ohmic contact.