Non-Polar GaN/AlN Superlattices on A-plane AlN (500nm) Buffer Layers Grown by RF-MBE
- PDF / 84,456 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 92 Downloads / 271 Views
E11.43.1
Non-Polar GaN/AlN Superlattices on A-plane AlN (500nm) Buffer Layers Grown by RF-MBE Takayuki Morita, Akihiko Kikuchi and Katsumi Kishino Department of Electrical and Electronics Engineering, Sophia University 7-1, Kioi-cho, Chiyoda-ku, Tokyo, 102-8554, Japan ABSTRUCT The growth conditions of A-plane AlN and GaN epitaxial layers by radio-frequency plasma assisted molecular beam epitaxy on R-plane sapphire substrates were investigated. The growth temperature and V/III supply ratio dependency on structural quality and surface roughness was described. The optimum V/III ratio for A-plane GaN and AlN layers was shifted to nitrogen rich side compared to the C-plane layers. A-plane GaN/AlN superlattices (SLs) were also grown on R-plane sapphire substrates. The X-ray diffraction peaks from a primary and a 1st satellite were observed. From a comparison of low temperature photoluminescence peak wavelength between A-plane and C-plane SLs, the built-in electrostatic field originated from spontaneous and piezoelectric polarization is negligible for A-plane SLs. INTRODUCTION GaN/Al(Ga)N heterostructure is one of the attractive material systems for various quantum effects device applications, due their large conduction band offset value up to 2 eV. Recently, intersubband transition (ISBT) at optical communication wavelength of 1.55 µm was realized by GaN/Al(Ga)N quantum wells [1-3]. Ultrafast carrier relaxation time of 140 fs of the GaN/AlN ISBT was also reported [4]. And room temperature observation of the negative differential resistance for GaN/AlN double barrier resonant tunneling diodes was also observed [5-6]. By use of these quantum effects, realization of some attractive devices, such as ultrafast optical switch, modulator, detector, and quantum cascade laser is expected. Usually, nitride-based epitaxial structures are grown on (0001) C-plane Al2O3 and (0001) C-plane SiC substrates along c-axis. Due to the noncentrosymmetric nature of wurtzite GaN/AlN grown in the (0001) direction, a strong built-in electrostatic field occurs perpendicular to the heterointerfaces because of spontaneous and piezoelectric polarization. Built-in electrostatic field brought about redshift of transition wavelength and reduction of recombination emission efficiency due to a reduction of the overlap of electron and hole wave functions. To avoid this problem, growth of A-plane quantum well is proposed [7-8]. Many reports on growth of A-plane nitride layers are presented. But A-plane epitaxial GaN layers tend to have a large number of threading dislocations and the surface morphology is rough compared to the C-plane GaN. For example, Craven et al. estimates that the threading dislocation density of A-plane GaN/AlN is approximately two orders of magnitude greater than that of C-plane GaN/AlN [9]. In this paper, we have grown some A-plane AlN, GaN and GaN/AlN SL layers on R-plane
E11.43.2
sapphire substrates. The effects of growth temperature and V/III supply ratio on the structural quality and surface roughness will be described. The ph
Data Loading...
