Thermodynamic Analysis and Purification for Source Materials in Sublimation Crystal Growth of Aluminum Nitride
- PDF / 135,955 Bytes
- 7 Pages / 595 x 842 pts (A4) Page_size
- 110 Downloads / 193 Views
1202-I05-08
Thermodynamic Analysis and Purification for Source Materials in Sublimation Crystal Growth of Aluminum Nitride Li. Du1 and J.H. Edgar1 1 Department of Chemical Engineering, Kansas State University Manhattan, KS 66506-5102, U.S.A. ABSTRACT Source material purification according to a thermodynamic analysis is reported for the sublimation crystal growth of aluminum nitride in an inert reactor. OAlOH is strongly favored over all other possible oxygen containing compounds in both the Al-O-H-N and Al-O-H-C-N systems, while Al2O the most favorable oxygen containing gas species for Al-O-N system, become secondary favorable gas species. A low temperature (1900˚C) source sintering with or without low temperature ( 1900˚C) sintering of AlN source can remove the oxygen from the solid phase. Temperature C 1.E+02
1200
1100
1000
Temperature C
900 1.E+00
Al
1200
1100
1000
900 Al
AlN
AlN
NO NO2 1.E-18
N2
Pressure atm
Pressure atm
1.E-07
Al2O
1.E-08
Al2O NO
1.E-14
NO2 N2
1.E-21
O
O
OAlOH
a
1.E-28 0.66
0.71
0.76
0.81
0.86
Reciprocal Temperature 1000/T(K)
OAlOH
1.E-28
b
0.66
0.71
0.76
0.81
0.86
Reciprocal Temperature 1000/T(K)
Figure 1: Partial pressure of the selected gas species in Al-O-H-N system; a, total pressure is 500 torr (0.658 atm); b, total pressure is 1 torr (0.001atm). Al-O-H-N system
Aluminum hydroxides are easily decomposed in the AlN source annealing process. For a total pressure of 500 torr (0.658 atm, Fig1a) and 1 torr (0.001 atm, high vacuum, Fig.1b), thermodynamics calculation predict that between 900 °C to 1200 °C, the major gas-phase species present are N2 and OAlOH. Although the Al vapor higher pressure is higher under vacuum (about 10-9), it is a minor gas species. Gas species Al2O, Al2, AlO, AlN, Al2O2, AlO2, NO, NO2, N2O, N3, O, O2 with pressure lower than 10-10 atm are negligible, while other gas species NO3, N2O3, N2O4, N2O5, O3, N, H2O, H2O2, HO, H2, AlH, OAlH, AlOH, H3N, H4H2, H2H2, H2N, HN, HNO, HONOc, HONOt, HONO2, with pressure lower than 10-28 atm are unlikely to be present in the vapor. While Al2O gas is only stable at high temperature (higher than 1900˚C), OAlOH gas is stable at lower temperature regardless of the ambient. In addition, the lower Al/O mole ratio in OAlOH (0.5) than Al2O (2) indicates less source mass is lost during the removal of oxygen from the solid phase. Al-O-C-H-N system
For the system with carbon, thermodynamic analysis shows that the major gas-phase species present are still N2 and OAlOH (with pressure of about 10-3). Consider carbon as a residual impurity in the as-received powder; figure 2a represents the partial pressure for the
gas species that has partial pressure higher than 10-13 at the calculated temperature range. Between 900 °C to 1200 °C, CO is a minor gas species (with a partial pressure between 10-6 -10-8). The addition of carbon does not change the concentrations of those species which are negligibly small in the Al-O-H-N system. Carbon containing species C2N2, C2N, C4N2, CNN, NCN, C, C2, C3, C4, C5, C3O2
Data Loading...
