Mg-doped N-polar InN Grown by RF-MBE
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0955-I08-01
Mg-doped N-polar InN Grown by RF-MBE Daisuke Muto1, Hiroyuki Naoi2, Shinya Takado1, Hyunseok Na2, Tsutomu Araki1, and Yasushi Nanishi1,2 1
Department of Photonics, Ritsumeikan Univ., 1-1-1 Noji-Higashi, Kusatsu, 525-8577, Japan
2
Center for Promotion of the COE Program, Ritsumeikan Univ., 1-1-1 Noji-Higashi, Kusatsu, 525-8577, Japan ABSTRACT We have investigated the growth properties of Mg-doped N-polar InN films grown by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). We found that the Mg-doped InN films had smaller grain size than non-doped films, and furthermore the grain size decreased with an increase in Mg doping amount. Non-doped InN exhibited a single X-ray diffraction (XRD) peak of (0002) h-InN. On the other hand, the Mg-doped InN produced a weak XRD peak of (111) c-InN in addition to a strong peak of (0002) h-InN. These results indicate that the Mg doping decreased the surface migration length of In atoms. From Hall-effect measurements, all the samples were shown to have n-type conductivity. Mg-doped InN grown with Mg cell temperatures of 130 and 135°C had carrier concentrations that were about half (i.e., ~4.5×1018 cm-3) that of the non-doped InN. However, the carrier concentration tended to increase with further supply of Mg. These results indicate that Mg-doping causes a trade-off between a carrier decreasing effect from the Mg acceptors and a carrier increasing effect from defects caused by the poor surface migration of In atoms.
INTRODUCTION InN is one of the most promising materials for use as a next generation semiconductor in long wavelength opto-electronic devices since it has smallest direct bandgap among the group III nitride semiconductors [1-3]. However, InN films of device quality have not yet been achieved because the films suffer from a high residual carrier concentrations and very high electron accumulation at the surface [4-6]. Therefore, it is still difficult to obtain p-type InN. Even though p-type doping of InN by Mg has been reported [7], it is difficult to precisely determine bulk conductivity of p-type layer because of a large electron accumulation at the surface. Another problem with p-type Mg-doped InN is that the growth mechanism of InN with Mg doping is not
Temp.
Thermal Cleaning 10 min
InN Intermediate
800 °C 530 °C
10 min
Nitridation 120 min
InN:Mg
280 °C RT
Figure 1. Growth time chart of Mg-doped InN.
60 min
LT-InN 10 min Time
well understood [8]. Moreover, in the case of GaN grown by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE), it was reported that the doping behavior of Mg strongly depends on the polarity of the films [9]. Mg-doped GaN grown on Ga-polar GaN exhibited a p-type conductivity, whereas Mg-doped GaN grown on N-polar GaN were highly resistive or semi-insulating. However, for InN, the effect of surface polarity on Mg doping has not yet been reported. In this study, we grew Mg-doped N-polar InN films by RF-MBE and investigated their properties.
EXPERIMENTAL DETAILS InN films were grown on (0001) sap
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