P-type Mg-doped GaN grown by molecular beam epitaxy using ammonia as the nitrogen source
- PDF / 287,014 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 57 Downloads / 205 Views
169
Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
As a viable alternative to MOCVD, MBE offers ease of control for the growth of multilayer structures, which is essential in high temperature electronics and optoelectronics applications. The growth of GaN by MBE has been intensively investigated in two ways; plasma-assisted MBE which employs N2 gas through a plasma source, 9 "10 and MBE which directly introduces nitrogen based gas such as NH3 as the nitrogen source. 11,12 In plasmaassisted MBE, p-type GaN is easily produced. However, the electrical and optical properties of the GaN films are often adversely affected by energetic ions. MBE employing ammonia as the nitrogen source avoids the ion damages due to the direct reactions between ammonia and gallium on a heated GaN surface. However, due to the different growth environments of MBE and MOCVD which both employ NH3 as the nitrogen source, p-type GaN grown by MBE could not be achieved using the same method employed in MOCVD. Only recently we have achieved ptype GaN grown by MBE using ammonia for the first time. 12 Unlike the MOCVD growth environment, the amount of hydrogen generated during MBE growth is small due to the direct surface reaction between Ga and ammonia in an ultra-high vacuum. The density of Mg-H complexes is thus much less in the Mg-doped GaN films grown by MBE using ammonia than those grown by MOCVD. However, the low density of Mg-H complexes in GaN films grown by MBE using ammonia as the nitrogen source may not be enough to circumvent the self4 compensation of GaN during growth. Our experiments show that Mg-doped GaN films grown by MBE employing ammonia were highly resistive but exhibited strong PL emissions. Unlike Mg-doped GaN grown by MOCVD, post-growth annealing was unable to reduce the resistivity of the Mg-doped GaN films grown by the MBE method using ammonia as the nitrogen source. In order to circumvent the self-compensation of GaN grown by MBE using ammonia as the nitrogen source, we discovered that the introduction of positive charges by employing an electron cyclotron resonance (ECR) nitrogen plasma during growth results in p-type GaN films. Positive charges could compensate the p-type dopant and raise the Fermi energy thus avoiding the formation of nitrogen vacancies during growth. This new MBE method avoids the problems caused by Mg-H complexes in the Mg-doped GaN films grown by MOCVD. High quality p-type GaN films, grown by this MBE method, have been obtained without post-growth annealing. At room temperature, hole density for these p-type GaN films was 4x10 17 cm- 3 while the mobility was 15 cm 2 /V-s. EXPERIMENT The growth was carried out in a MBE system equipped with an ECR plasma source, an ammonia feeding line, and conventional Knudsen cells of Ga, Al and Mg. The applied ECR microwave power was 20 W. The growth rate of GaN was varied between 0.2 gm/hr to 1
170
ltm/hr, as calibrated after growth by infrared interference spectra measured from Fourier transform infrared spectroscopy (FTIR). The beam flu
Data Loading...
