Properties of Bi-doped PbTe layers grown by liquid phase epitaxy under controlled Te vapor pressure

Abstract

Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, x Bi , lower than 0.2 at.%, an excess deep-donor level (activation energy E d Ϸ 0.03-0.04 eV) appears, and Hall mobility is low. In contrast, for x Bi Ͼ 0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 10 17 cm Ϫ3 . Inductive coupled plasma (ICP) emission analysis shows that, for x Bi ϭ 1 at.%, Bi concentration in the epitaxial layer is as high as N Bi ϭ 2.3-2.7 ϫ 10 19 cm Ϫ3 . These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bidoped layers shows a minimum at a Te vapor pressure of 2.2 ϫ 10 Ϫ5 torr for growth temperature 470ºC, which is coincident with that of the undoped PbTe.

Mid-infrared photoconductive properties of heavily Bi-doped PbTe p–n homojunction diode grown by liquid-phase epitaxy

“…The reverse bias is 1.0 V. From the straight line portion of the graph, the activation energy of the dark current was obtained as 0.067 eV. This deep level energy was not revealed in Hall Effect measurements of heavily Bi-doped epitaxial layers in our previous study [5]. Therefore we assumed that the deep level is sourced from the PbTe p-n junction; in particular, from the Tl-doped p-side layer.…”

“…The photocurrent density of the heavily Bi-doped sample is approximately 20 times and 3 times greater than that of the undoped sample and heavily In-doped sample, respectively. Since PbTe systems are characterized by a high electric constant (e = 1400-1800) [11], we previously assumed that the high Bi concentration induced strong self-compensation, reducing the number of free electrons and the wide depletion layer [4,5]. Moreover, the free electrons in the n-type layer absorb less infrared radiation in heavily Bi-doped materials than in the other evaluated materials.…”

“…In particular, we studied the behavior of dopant impurities (such as thallium, bismuth and indium) in PbTe bulk crystal and the epitaxial layer [4][5][6][7]. Our previous studies also reported the electrical and optical properties of heavily Bi-doped (Bi concentration x Bi % 2 Â 10 19 cm À3 ) n-PbTe and Tl-doped p-PbTe epitaxial layers grown by TDM-CVP LPE [4,5]. We proposed that a Bi donor atom forms a donor-acceptor (DA) pair with a neighboring or near-neighbor Bi acceptor atom.…”

“…We proposed that a Bi donor atom forms a donor-acceptor (DA) pair with a neighboring or near-neighbor Bi acceptor atom. Such DA pairs cause no effective ionic scattering and form no deep level at high Bi concentrations [4,5]. In the present study, we fabricate and investigate a mid-infrared photodiode based on heavily Bi-doped PbTe, and determine its characteristics.…”

Electroluminescence and lasing properties of highly Bi-doped PbTe epitaxial layers grown by temperature difference method under controlled vapor pressure

“…6 From these results, it is suggested that at high Bi concentration, a Bi-donor atom located at the Pb site and a Bi-acceptor atom make a nearestneighbor or very near donor-acceptor (DA) pair, which does not cause effective ionic scattering nor form a deep level. Also, Bi impurities form deep levels with E d ϭ 0.06Ϫ0.08 eV, only at a relatively low Biconcentration region, i.e., x Bi Ͻ 0.2 at.%, or, for Te vapor pressure exceeding the optimum value for stoichiometry.…”