N-type, germanium

Fig. S-. Photopotentia] observed for n-fype and p-fype semiconductor electrodes of germanium as a function of electrode potential El, = flat band potential of n-type germanium band potential of p-type germanium. [From Pleskov, 1980.]...

Fig. 5.2 Variation of the activation energies el9 e2 and e3 with distance a between donors for n-type germanium (Davis and Compton 1965). For e3 the calculations of Miller and Abrahams for K—0.04 are shown (full curve).

Zabrodskii and Zinov eva (1984) found that in n-type germanium the transition can be induced by increasing the compensation, which is consistent with the above argument. They found hopping conduction with v=j on the insulating side, with the Coulomb gap tending to zero at the transition, as noted in Chapter 1, Section 15... 

Four n-type germanium crystals of differing resistivities and one p-type were chosen for this initial investigation. 1-Propanol was chosen as the adsorbate. Before the results of the adsorption measurements are summarized, it seems desirable to review briefly some of the pertinent information already available concerning the surface of germanium. 

Figure 2. Chemisorption of propanol on n-type germanium samples of different resistivities as a function of activation temperature...

Systematic variations in lifetime and conductivity as a function of the ambient were obtained on n-type germanium. 

Redox reactions can be studied at germanium electrodes, undergoing no rapid dissolution or hydrogen evolution, only in a region of polarization over approximately 0.9 volts. Under high currents the assumptions of electronic equilibrium in the interior of the semiconductor are not valid (compare the limited hole current at n-type germanium in the region of dissolution). 

The results of the measurements with intrinsic, p-, and n-type germanium (N = 3.5 x 10 cm 3, Np = 7, 5 x l(r cm ) in IN KOH at 25° and 45°C are shown in Figs. 3-5. The circular frequency, w =2irf, used for the measurement is indicated at each curve. Ail measurements were made with and without illumination of the electrodes. The capacity-potential curve... 

This is exactly the same expression as for the diffuse part of the double layer in an electrolyte (1). Under the same assumptions, the capacity ofan n-type germanium electrode Is given by... 

If the hole concent ration in the semiconductor is relatively low, as in low resistivity n-type germanium or silicon, the available holes in the surface region are used up at low current densities and the etch rate is slow. The anodic current under these conditions can be increased by providing additional holes at the surface. Holes produced as a result of illuminating the semiconductor give uniform electrolytic etching on n-type semiconductors. Germanium is electro-lytically etched in several electrolytes while silicon can only be dissolved anodically in fluoride solutions. A thick film of amorphous silicon forms on silicon anodes in acid fluoride solutions below a critical current density. 

The data of Efimov and Erusalimchik (5) shown in Fig.l give an example of the different current-voltage characteristics obtained with various resistivity n- and p-type germanium electrodes made anode in 0.1 N HC1. Brattain and Garrett (4) and others (7-10), however, found much lower saturation current densities by one to two orders of magnitude with n-type germanium made anode in similar electrolytes. Similar curves for n-type silicon would show saturation current densities in the order of microamperes per square centimeter. 

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. 

Fig. 2. Temperature variation of the saturation current of a barrier between 5,5 ohm-cm n-type germanium and 10 percent KOH solution.

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... 

Electrolytic etching has been used to reveal p-n junctions (43) as well as to remove n- or p-type material preferentially from diodes and transistors (28). These processes make use of the rectifying barrier of p-n junctions as well as the hole depletion effect at the surface of n-type germanium and silicon. 

Dewald s results are in variance with those of Cretella and Catos (8), who reported that in nitric acid concentrations up to 4N, p-type germanium reacts twice as rapidly as n-type germanium. In view of this discrepancy, the earlier experiments were repeated and extended. The new results (hitherto unpublished) are shown in Fig. 8. It is seen,for resistivities... 

Fig. 5.31. (a) p-type germanium detector (b) n-type germanium detector (c) planar germanium detector ... 

If the detector crystal is made of n-type germanium, the outer electrode can be made rather thin. Include a thin aluminium or a beryllium window at the face of the detector, so that low energy electromagnetic radiation will be able to enter the volume of the detector, and you get a gamma ray detector that is good also for soft gamma rays, and X-rays. 

Figure 7.10 (a) Electron mobility versus temperature for n-type germanium, (b) Hole mobility versus temperature for p-type germanium (from Ref. 4). 

A 1-cm cube of n-type germanium supports a current of 6.4 mA when a voltage is applied across two parallel faces. The charge carriers have a mobility of 0.39 m s Determine the Hall coefficient of the crystal assuming that only the majority charge carriers need be considered. 

These basic properties of semiconductor electrodes were observed at first by Brattain and Garrett with germanium electrodes. It was further shown for germanium that the small cathodic current at p-type and small anodic current at n-type germanium are quantitatively determined by the diffusion of minority carriers. ... 

Ever since the first reports of optical studies of electrochemical systems, efforts have been made to obtain infrared spectra of reaction intermediates and adsorbates. The earliest studies were based on total internal reflection using an n-type germanium electrode (transparent to IR radiation), and OTTLE systems using gold minigrids sandwiched between NaCl plates. These were not particularly successful, however, and it is only recently that these configurations have again been used, this time for Fourier Transform spectroscopy [29,30]. Undoubtedly the most successful technique has been potential modulated external reflectance IR spectroscopy [31]. 

On the other hand, five valent impurities, such as arsenic or phosphorus, will have one electron in excess of that required for electronic uniformity. The impurity atom will be a donor atom sitting in a donor site and will introduce donor states just below the conduction band. Germanium with such impurities is n-type germanium ( n for negative donor impurities). 

Figure 3.10 Calculated shapes of the rising edges of an n-type germanium detector for interactions at different points within a coaxial detector (a) near to core (b) mid-way (c) near to outside...

Figare 3Jt. Knoop hardness versus inden-ter angle for n-type germanium at two temperatures. After Roberts et This anisotropy is like that in Figure 3.7. 

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