• PDF / 46,975 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 94 Downloads / 242 Views

DOWNLOAD

REPORT

---

Thermal and Electrical Properties of Czochralski Grown GeSi Single Crystals

Ichiro Yonenaga, Takaya Akashi, and Takashi Goto Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan ABSTRACT Single crystals of Ge1-xSix alloys in the composition range 0 < x < 1 non-doped and doped with boron, gallium, and phosphorus as an impurity were grown by the Czochralski method. The measurements of the thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (α) of the grown crystals were performed in the temperature range 300 – 1000 K. The thermal conductivity κ shows a minimum (κ ~ 3.5 W/K･m) around the Si content x = 0.5 - 0.7, which can be explained by the phonon scattering due to a distortion of the crystal lattice. The Seebeck coefficient α was 300 - 400 µV/K at 600˚C in the impurity-doped GeSi alloys. An |α| vs ln (σ) plot of highly impurity-doped GeSi alloys obeys a linear relation. The slope of the straight line is 1.2 k/e, indicating the coorporation of the charged impurity into the alloy scattering mechanism.

INTRODUCTION Germanium-silicon Ge1-xSix alloy is well known as a material for thermoelectric power generators at elevated temperatures 800 –1200 K. In fact, GeSi thermoelectric devices have been successfully used as a power generator with radioisotope in deep space probes Voyager, Galileo, etc. Up to now, the thermoelectric properties were measured on materials of highly doped and with limited compositions as reported by Abeles [1], Dismukes et al. [2] and Abrikosov et al. [3] in the 1960s. In the experimental works, however, the aim was to increase the magnitude of figure of merit as a thermoelectric element, and thus, materials with poor qualitative crystallinity in disturbed system have been investigated widely similar to other thermoelectric materials. Usually GeSi alloys for such works were prepared by the zone leveling method or by hot pressing or sintering of powder materials. Maximum figure of merit in GeSi alloy has been discussed theoretically by some groups [4, 5]. Slack and Hussain have suggested that a high quality single crystal of GeSi alloy might be the most useful material for no boundary scattering effect [5]. In order to verify such a theoretical expectation, it is necessary to use bulk crystals of GeSi alloy with high quality. In addition, it is quite important to know the intrinsic properties of GeSi alloys in the whole composition range to understand the thermoelectric mechanism in terms of the carrier transport and scattering mechanisms in alloy semiconductors. In this viewpoint we started to investigate thermoelectric parameters of single crystal GeSi alloys grown by the Czochralski technique and reported the preliminary results [6,7]. This paper reports on the recent results on the subject. The thermal conductivity, electrical conductivity and Seebeck coefficient (thermoelectric power) of B-, Ga-, and P-doped single crystals of Ge1-xSix alloys in the whole composition 0 < x < 1 were investigated at 300 – 1000 K. G7.4.1

Both the dilute alloy cr