Germanium hole concentration

A typical featnre of reactions involving the minority carriers are the limiting currents developing when the snrface concentration of these carriers has dropped to zero and they mnst be snpplied by slow dilfnsion from the bulk of the semiconductor. A reaction of this type, which has been stndied in detail, is the anodic dissolution of germanium. Holes are involved in the first step of this reaction Ge — Ge(II), and electrons in the second Ge(ll) —> Ge(IV). The overall reaction equation can be written as... 

It can be seen from Fig. 14.7 that the polarization curve for this reaction involving p-type germanium in 0.1 M HCl is the usual Tafel straight-line plot with a slope of about 0.12 V. For -type germanium, where the hole concentration is low, the curve looks the same at low current densities. However, at current densities of about 50 AJvcF we see a strong shift of potential in the positive direction, and a distinct limiting current is attained. Thus, here the first reaction step is inhibited by slow supply of holes to the reaction zone. 

Fig. 4. Arrhenius plot of the free hole concentration in a beryllium-doped germanium crystal grown in a hydrogen atmosphere. The shallow acceptor A(Be,H), present at a concentration of 1013 cm-3, is shown to dissociate under thermal annealing. 

Fig. 9. Arrhenius plots of the free hole concentration p (log p versus 1000/T) in two samples cut from a partially dislocated slice of ultra-pure germanium. The dislocation-free sample contains an acceptor with Ev + 80 meV. The shallow level net-concentration is the same in both samples.

Germanium used for transistors has a resistivity of 2 cm and an electron hole concentration of 1.9 x 10 holes/cm. (a) What is the mobility of the electron holes in the germanium (b) What impurity element could be added to germanium to create electron holes ... 

Germanium and silicon are electrolytically etched at about the same rate, about 3x10" 5 cm 3/coulomb. Thus at a current density of 500 ma/crn, Ge and Si are dissolved at the rate of about 1.7x10 cm/sec (0.0004 in /min). In order to electrolytically etch n-type semiconductors at a reasonable rate, some means must be found to increase the hole concentration at... 

The equilibrium hole concentration can be increased by raising the temperature of the semiconductor. Uhlir (7) found that the temperature variation of the saturation current density across the barrier between anodic n-type germanium and 10% potassium hydroxide solution is quite like that of a p-n junction. About a tenfold increase in the saturation current density is obtained for each 30° C rise in temperature as shown in Fig. 2. 

This method is most effective with n-type germanium where the equilibrium hole concentration is low. Selective etching was produced either by focusing light on the surface to create... 

This expression is derived from the more general case where the electron and hole concentrations in the conduction and valence bands are n and p with np = n2. At RT, taken as 300 K, the intrinsic carrier concentration n is 1.1 x 10111 cm in silicon, but it increases to about 4 x 1013 cm 3 in germanium to reach 2 x 1016 cm-3 in intrinsic InSb. 

Impurity Semiconductors, n-Type andp-Type. The discussion has been restricted so far to pure intrinsic semiconductors exemplified by germanium and silicon. In these substances, there is a low concentration of charge carriers (compared with metals). Further, the hole and electron concentrations are equal, and their product is a constant given by the law of mass action... 

If, however, the electrode is a semiconductor, the distribution of charges in the solid will be similar to that in the electrolyte, for the concentration of carriers in semiconductors is significantly smaller than in metals, hi pure germanium for example the concentration of electrons and holes at room temperature is 2.5 x 10 cm or 4 x 10 mole/1 i.e., the... 

The number of intrinsic electrons in pure germanium at 300 K is 2.4 x 10 m . The material is doped with a concentration of phosphoms donors of 10 phosphorus atoms per metre cubed. What is the equilibrium concentration of electrons and holes ... 

Germanium (Ge). Low-field electronic transport is provided by electrons in the minima of the conduction band and holes near the Fg point in the valence bands. At room temperature, the mobUity of samples with impurity concentrations below 10 cm is Umited essentially by lattice scattering higher donor or acceptor concen-... 

Figure 18.16 plots the logarithm of the intrinsic carrier concentration n, versus temperature for both silicon and germanium. A couple of features of this plot are worth noting. First, the concentrations of electrons and holes increase with temperature because, with rising temperature, more thermal energy is available to excite electrons from the valence to the conduction band (per Figure 18.6h). In addition, at all temperatures, carrier concentration in Ge is greater than in Si. This effect is due to germanium s smaller band gap (0.67 vs. 1.11 eV, Table 18.3) thus, for Ge, at any given temperature, more electrons will be excited across its band gap.

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