n-Type Doping of Diamond
- PDF / 253,046 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 221 Views
0956-J04-01
n-Type Doping of Diamond Satoshi Koizumi Optical Sensor Group, NIMS, 1-1 Namiki, Tsukuba, 305-0044, Japan
ABSTRACT n-Type doping of diamond is one of the most important issues for electronic application of diamond. Phosphorus is the best candidate as an n-type dopant at this moment. We have succeeded to grow high quality phosphorus doped diamond thin films on {111} diamond substrates. Although the ionization energy of phosphorus donor is large (0.57 eV), the n-type conductivity is clearly observed by Hall measurements. The Hall mobility is as high as 660 cm2/V-sec at room temperature. In this paper, current status of n-type diamond research are mentioned mainly focused on the growth of high mobility n-type diamond and its electrical properties. The Hall measurements performed in a wide temperature range gives detailed information about the n-type conductivity nature of phosphorus doped diamond.
INTRODUCTION From early 1980’s, whereas the chemical vapor deposition (CVD) technique was introduced for diamond growth, n-type doping has been investigated mainly doping phosphorus (P) as an impurity. Nitrogen does not give any shallow donor levels due to the local lattice deformation that is known as Jahn-Teller effect when single nitrogen atoms are doped at the lattice substitutional sites. The theoretical calculation (effective mass approximation) predicted the ground state of P atom situated at about 200 meV below the conduction band minimum in diamond [1]. Although some studies have shown electrical conductivity, the evidence of the ntype conductivity was lacking because of the polycrystalline nature of the samples which involves various kinds of conduction routs such as grain boundaries, defects and graphitic aggregates [2, 3, 4]. There were no report about the nature of P atoms in diamond as the n-type dopant. It was needed to clarify the validity of P-doping on n-type diamond formation by applying Hall effect measurements intensively for high crystalline perfection P-doped diamond layers grown epitaxially. In 1996, we have succeeded to grow n-type P-doped diamond thin films on diamond substrates and the conductivity nature was characterized clearly by temperature dependent Hall measurements [5]. The P-doped layers have been grown on synthetic Ib diamond substrates with the crystalline orientation of {111}. On {100} orientated substrates, it was impossible to grow n-type layers nor flat epitaxial films [6, 7, 8]. The situation is opposite to the conventional experimental results on undoped or boron doped CVD diamonds that {100} surface can be formed less defective than {111}. It is very interesting such a small amount of impurity atoms introduced for doping can give such a big influence to the diamond growth itself. The activation energy of carrier concentration was 0.43 eV in the first report. However the value was underestimated because the temperature dependence of carrier concentration included the influences of hopping conductivity due to heavily doping and also crystalline defects. The activation
Data Loading...
