One of the authors of the present paper has proved that oxygen affects the semiconductor properties of SnTe and other substances /l/. This was taken into consideration in /2/ where SnTe was synthesized in alumina ceramics (quasi-closed volume) from outgassed Sn (5 N) and Te (6 N). The single crystals, grown by horizontal crystallization, had low current c a r r i e r concentrations p = (0.39 to 0. 41)x1O2' cm-3 (p = l/q %, where q is the electron charge and % the Hall coefficient), and great values of the product % d= = 915 to 950 cm /Vs at 300 K /2/. 2
The temperature dependence of the current carrier mobility in PbTe (77 to 550 K) is not explained yet and for PbTe(I) (synthesized by an iodide method) is not examined at all. This method is combined with the travelling heater method to grow crystals from Te solution at 550 °C with a growth rate of 90 and 60 μm/h. The important results are: 1) effective purification (the components have purity about 3N), 2) extremely high mobilities of 20000 to 40000 cm2/Vs at 77 K. The material is only n‐type with concentration n ≈︁ (I to 2) × 1018 cm−3 which is constant from 77 to 450 K. In the interval 77 to 160 K, μ∼ T−a and a depends very simply on the ratio of the difference and the sum of the vacancy concentrations. In the interval 180 to 450 K, μ decreases exponentially like a probability law. These results are explained by a model of thermal generation of Frenkel pairs from iodine atom shifting (I atoms occupy Te lattice sites). An iodine Frenkel pair acts like a simple donor.
The well known increase of the Hall coefficient with temperature in SnTe is usually explained bythe double valence band model. SnTe is synthesized and crystallized by various methods. In the concentration interval of carriers of 4 × 1019 to 5 × 1020 cm−3 it is often found, that the curves RH(T) are crossed, a fact, which cannot be explained with the model above mentioned. A model of thermally generated Frenkel‐type defects of Te‐atoms is proposed. As result of the generation hole traps occur with two distinct energy levels. The low‐temperature level depends on carrier concentration (on the concentration differences between the vacancies of Sn and Te). The high temperature level is connected with the dopands. The exponent a in the temperature dependence of mobility, μ ∽ T−a in the range. RH = const depends elementarily on the compensation coefficient (ratio of the concentrations of the tellur and tin vacancies).
R( T), der differentiellen Therniokraft a( T) und dnsXernst-Ettingshauaen-Koeffizient.cn Ql (T) wurden im Temperaturbereich zwischen 100 und 600 "K an natiirlichen Hleisulfidkristallen (mit n N 3 . 10l5 untersucht. Die Breite der vcrbotenen Zone bei T = 0 betragt 0,34 eV und das I~emeglichkeitsvcrhaltnis pn/,up = 1,4. Im Eigenleitungsgebiet ist die Hallbeweglichkeit proportional T-312, im Oebict vollstiindiger Ionisation der Donatoren ist sie proportional T-2. Bei tiefen Tempcraturen tritt ein Phononen-Drag auf. Die aus den MeBwerten berechnete effektive Masse ist proportional T0,Z. Die Lebensdauer 7p der injizierten Trager variiert zwischen 20 und 60ps und stimmt mit den von SCAKLON [GI erlialtenen Werten iiberein.
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