Depletion region

A space charge zone ( RLZ ), also called depletion layer or barrier layer in the transition between differently doped semiconductors is an area in which space charges with excess and lack of charge carriers are facing, so that this zone appears charge neutral at equilibrium to the outside. Depending on the polarity of an externally applied electric voltage, linked so that different electric field configurations result in the depletion zone, this area in the semiconductor is good or only very weakly electrically conductive. This physical effect is the basis for the rectifying function of the semiconductor device of a diode dar. side diodes play space charge zones in other electronic devices such as bipolar transistors or junction field- effect transistors have a fundamental role.

Formation

When two different doped semiconductor material, an n- and a p-type semiconductor are brought together spatially closely results in a so-called pn junction. In the n- region is an excess of negatively charged electrons in front of, in the p-type region, an excess of positively charged hole- also as a hole designated positively charged impurities in the Halbkleiterkristall. By the concentration gradient of charge carriers in the transition region between the n-and p-type region results in a diffusion of carriers: electrons from the n region migrate to the p -type semiconductor, electron holes diffuse in the n-doped semiconductor. The charge carriers recombine there with the other type of charge carrier.

In total, thus forming in the transition region in the p-type semiconductor, an excess of negative space charge in the n-type semiconductor, an excess of positive space charge, the depleted space-charge region thus formed according to the recombination of free ( movable ) charge carriers. The thus formed electric field in the space charge zone counteracts a further diffusion of charge carriers from the two zones since the field produces an opposite drift current. It forms an equilibrium case in which diffusion current and drift current of charge carriers hold the balance, as in the illustration on the spatial distribution and displayed in the field profile. Since diffusion processes are strongly temperature dependent, the size of the space charge region as a result of changes in temperature changed. From the outside, the residual maturity of field-free equilibrium. There is no potential gradient of the charge carriers transported across it.

Is applied to the two semiconductor layers from the outside an electric voltage, and this voltage gives an additional electric field in the semiconductor, which is superimposed on the electric field of the space charge region in the case of equilibrium, can be divided into two substantially cases which, as for the basic functions of electronic components diodes are decisive:

Space charge regions are formed in addition to n -and p- doped semiconductors also at metal-semiconductor contacts and can lead to rectifying behavior of these contacts, the so-called Schottky contact which in Schottky diodes is applied. Due to the high number of free electrons in the metal, the space charge zone is limited however, almost all of the corresponding semiconductor region.