Co-Doping Characteristics of Si and Zn with Mg in P-type GaN
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F99W3.84
RESULTS AND DISCUSSION Mg doped GaN In order to investigate Mg doping characteristics in GaN, several kinds of GaN films with different hole concentrations obtained by varying the amount of Cp2Mg flow rate were grown. Figure 1 shows typical Hall characteristics of the GaN films as a function of gas phase [Mg]/[Ga] ratio measured at room temperature after post-growth rapid thermal annealing (RTA) in N2 ambient for 30 s at 900 oC. Electrical characteristics were evaluated using the conventional van der Pauw Hall measurement in which magnetic field of 0.5 Tesla and currents between 10 and 100 uA are applied. The GaN grown under a [Mg]/[Ga] ratio of 5.4 10-3 gives a high resistivity of 5.6 cm and a 16 -3 low hole concentration of 7.3 10 cm . When the [Mg]/[Ga] ratio is reached to 7.6 10-3, the hole concentration and resistivity abruptly change and have the maximum value of 6.7 1017 cm-3 and the minimum value of 0.8 cm, respectively. If the [Mg]/[Ga] ratio is larger than 7.6 10-3, the hole concentration is gradually decreased and the resestivity is increased. 10
10
p-type n-type
1
17
10
Resistivity (Ohm-cm)
Hole Concentration (cm-3)
1
Resistivity (Ohm-cm)
Hole Concentration (cm-3)
1E17
1E16
18
10
1E18
0.00 0.03 0.06 0.09 0.12 0.15 0.01
SiH4 Flow Rate (nmol/min)
[Mg]/[Ga] Ratio
Figure 1, Dependence of resistivity (solid circle) and hole concentration (open circle) at room temperature on the gas phase [Mg]/[Ga] ratio during the growth of GaN.
Figure 2, The resistivities (solid circles) and hole concentrations (open circles) as a function of SiH4 flow rate during the growth under the constant [Mg]/[Ga] ratio of 7.6 10-3.
Mg-Si co-doped GaN For the purpose of studying Si co-doping characteristics in Mg doped GaN films, some kinds of specimens with different SiH4 flow rates were grown where the [Mg]/[Ga] ratio was kept constant to 7.6 10-3 thought to be the optimum condition. The Hall characteristics of the samples as a function of SiH4 flow rate are exhibited in Fig. 2, which are carried out after the identical RTA treatment as mentioned earlier. The Si and Mg co-doped p-type GaN layers show anomalous electrical behaviors. If considering only absolute net acceptor and donor concentrations, one can easily predict that hole
F99W3.84
(a)
[Mg]/[Ga] : 3.6 X 10-2
1.8 X 10-2
7.6 X 10-3
5.4 X 10-3
2.0
2.5
3.0
3.5
Normalized PL Intensity (arb. units)
Normalized PL Intensity (arb. units)
concentrations are gradually decreased with increasing SiH4 flow rate, and finally type conversion arises. However, actual experimental data do not follow our expectation. In other words, the hole concentrations are increased as SiH4 flow rates increase before occurring type conversion. It is also interesting fact that type conversion occurs at a SiH4 flow rate of 0.13 nmol/min, because this value is the quantity corresponding to the doping level of 1 1017 cm-3 when applied in an undoped GaN. In addition, the maximum hole concentration (4.5 1017 cm-3) of p-GaN co-doped with Si and Mg shows the lower 1017 cm
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