Thermoelectric and Electrical Properties of InSb Thin Films Prepared by Metalorganic Chemical Vapor Deposition
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0980-II05-42
Thermoelectric and Electrical Properties of InSb Thin Films Prepared by Metalorganic Chemical Vapor Deposition Masashi Matsumoto, Jun Yamazaki, and Shigeo Yamaguchi Kanagawa University, Yokohama, 221-8686, Japan
ABSTRACT We studied the thermoelectric and electrical properties of InSb thin films prepared by metalorganic chemical vapor deposition. The thermoelectric properties were evaluated using power factor (Pf =α2/ρ), which is an important criterion, and a value of 10-3 W/mK2 is a standard for practical use. Maximum value of Pf was 2.4×10-3W/mK2 at 600K for 1-µm-thick InSb, 3.4×10-3W/mK2 at 600K for 3-µm-thick InSb, and 5.8×10-3W/mK2 at 600K for 5-µm-thick InSb. On the other hand, the maximum Pf of bulk-InSb was 5.4×10-3W/mK2 at 600K. INTRODUCTION InSb has been mainly used for infrared detectors and Hall sensors1. However, we have recently demonstrated that InSb is a very promising candidate as a thermoelectric power material2. In this study, we have focused on the results on the basis of thermoelectric properties of InSb thin films. The use of unused thermal energy such as wasted heat in the environment is important from a viewpoint of energy and environmental problems. Thermoelectric conversion can directly change heat energy into electric energy, and does not need movable parts and not produce radiation such as radioactive material. On the other hand, many electric devices have been integrated and downsized, and the technology to achieve low power supplies will be necessary. To operate such small-size devices, the power source is very important. In particular in terms of use of human body heat, we have studied thermoelectric power devices. We have used InSb because this material has the highest electron mobility (78000 cm2/Vs at room temperature (RT)) among III-V compounds, and this feature plays an essential role when the rapid response to external signal is needed. EXPERIMENT In this study, InSb films were deposited on sapphire (0001) substrate with InAs interlayer as buffer layer by metalorganic chemical vapor deposition (MOCVD). Trimethylindium (TMIn), Trimethylantimony (TMSb) and Tertiarybutylarsine (TBAs) were used as sources, and H2 was used as carrier gas. The InAs interlayer served as wetting layer because the wetting of InSb to sapphire is very poor. The thickness of InAs was 15 nm. The thicknesses of InSb thin films were 1.0µm, 3.0µm and 5.0µm. We have adopted sapphire as substrate due to the following reasons. 1) in most cases, InSb thin films have been deposited on semi-insulating GaAs (001) substrate. However, even if GaAs is semi-insulating at RT, carrier injection from GaAs into InSb occurs at
higher temperatures. This phenomenon will make the origin properties of InSb misunderstood. 2) lattice-mismatch between InSb and sapphire (0001) (3.7%) is much smaller than that between InSb and GaAs (001) (15%). And the bulk-InSb (111) was also measured as a reference for InSb thin films grown by MOCVD. The thickness of bulk-InSb was 450µm. Table 1 shows our growth condition.
InAs InSb
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