A Critical Comparison Between MOVPE and MBE Growth of III-V Nitride Semiconductor Materials for Opto-Electronic Device A
- PDF / 2,485,237 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 90 Downloads / 144 Views
Downloaded from https://www.cambridge.org/core. IP address: 5.101.222.175, on 14 Feb 2019 at 08:24:41, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300003100
First is the difference in the epilayer growth morphology; second is the doping of GaN with magnesium for p-type conductivity; and finally, the deposition of InGaN quantum wells with compositions in the visible emission range. This comparison provides a twofold benefit of identifying critical areas for further exploration in crystal growth and deepening the understanding of the underlying physical processes at work in successful epitaxial deposition. EXPERIMENTAL PROCEDURE MOVPE growth was performed in a vertical flow rotating wafer (up to 2000 rpm) system designed and built at NCSU. A radiatively heated substrate mount, of original high reliability design, can achieve temperatures up to 1200°C, as measured by an optical pyrometer. 50-mm diameter sapphire wafers were used as the base substrate with a typical low temperature GaN nucleation layer. Trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMI) and ammonia were used as precursors with nitrogen and hydrogen carrier gases at a reactor pressure of 76 Torr. Silane and bis(cyclopentadienyl) magnesium were used as dopant sources. Growth temperatures for GaN ranged from 1060°C to 1130°C. The conditions resulted in 2D epitaxial growth at rates of 1-2 µm/hr. InGaN growth was conducted in a manner similar to Yoshimoto at temperatures from 725°C to 800°C [12]. MBE growth was performed in an EPI Model 930 system using elemental group III and dopant sources. Rf plasma sources were used to generate the active nitrogen species. Prenucleated GaN/SiC substrates were used for the MBE deposition. Growth temperatures ranged from 750°C to 900°C for GaN and 670°C to 700°C for InGaN resulting in growth rates of 0.4-2 µm/hr. A modulated beam technique was used to grow InGaN as previously described [11]. The MOVPE and MBE were connected as a multichamber UHV cluster tool. This allows for the growth of sophisticated heterostructures with specific layers grown in either the MBE or MOVPE system where applicable. Characterization of epitaxial layers included: scanning electron microscopy using a JEOL JSM6400 SEM, photoluminescence (PL) using a 12 mW He-Cd laser source, and Nomarski microscopy using an Olympus BX60 microscope and image capture system. Vertical cross section samples were studied in a Topcon 002B Transmission Electron Microscope (TEM) with g=(1100) at 200 kV. LED samples were prepared following standard lithography techniques and using Ni/Au and Ti/Al as p-type and n-type contact metals, respectively. RESULTS AND DISCUSSION Epitaxial Layer Surface Morphology and Magnesium Doping The surface morphology of epitaxially grown GaN exhibits an obvious difference between MOVPE and MBE deposited material. As shown in the SEM micrograph in Figure 1a, undoped or n-type doped MBE grown GaN exhibits a “wormy” structure. This surface
Data Loading...
