研究目的
The purpose of this study is to improve the contact film properties by deposition and annealing and to produce ohmic contact characteristics with a low resistance.
研究成果
The as-deposited films are amorphous in the chemical compositions (ternary Ti–Si–C system). All the as-deposited films show non-ohmic contact properties. Electrical properties are different between the Ga- and N-faces in n-type GaN. For n-type GaN, the contact films with the composition of Ti:Si:C = 57:24:19 in at% (sample 1) show ohmic properties after annealing. The TiN phase forms at the contact interface of sample 1 by annealing at 873 K for 60 s. The TiN phase causes an ohmic contact for n-type GaN. For p-type GaN, the electrical properties of sample 5 with a composition of Ti:Si:C = 42:34:24 in at% in the three-phase coexistence region were improved after annealing, but a good ohmic contact was not obtained.
研究不足
The ohmic contact was not obtained for p-type GaN although the I–V properties were improved by annealing. The p-type GaN grown by MOCVD contains hydrogen (H) atoms, which decrease the electrical properties. H release from GaN is necessary by the annealing process. GaN tends to be resolved at high temperatures, and N-vacancies form. Over-annealing converts the main carriers from holes to electrons (i.e., changes the material from p-type to n-type).
1：Experimental Design and Method Selection:
Ternary Ti–Si–C amorphous films with various chemical compositions were formed by the radio frequency magnetron sputtering method. The compositions were controlled by changing the number of target plates of Ti, Si, and C.
2：Sample Selection and Data Sources:
Single-crystal substrates of n-type GaN were made by the laser lift-off technique. For the p-type GaN specimens, undoped GaN crystal and Mg-doped p-type GaN crystal were epitaxially grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD).
3：List of Experimental Equipment and Materials:
Radio frequency magnetron sputtering apparatus, high-purity Ar gas, Al mask, infrared-heating vacuum furnace.
4：Experimental Procedures and Operational Workflow:
After setting the GaN specimens and targets in the sputtering apparatus, the chamber was evacuated and high-purity Ar gas was introduced. Ti–Si–C thin films were sputter-deposited on the GaN substrates after sputter-cleaning. Two contact pads were formed by using an Al mask in each sample. The annealing was carried out at 873 K for 60 s by an infrared-heating vacuum furnace.
5：Data Analysis Methods:
The current–voltage (I–V) characteristics between the two contact pads were measured by a conventional method using a stabilized DC power supply. The microstructures of the contact films were analyzed by X-ray diffractometry (XRD) and transmission electron microscopy (TEM).
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