Probing the formation of two-dimensional electron gas in AlInGaN/GaN heterostructures by photoluminescence spectroscopy
- PDF / 2,907,569 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 153 Views
E3.43.1
Probing the formation of two-dimensional electron gas in AlInGaN/ GaN heterostructures by photoluminescence spectroscopy C. B. Soh1,2, W. Liu2 , S. J. Chua#1,2 S. Tripathy2 and D. Z. Chi2 1
Centre of Optoelectronics, Department of Electrical and Computer Engineering, National University of Singapore, 2 Engineering Drive 3, Singapore 117576 2 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602 ABSTRACT Using temperature-dependent photoluminescence (PL), we report a detailed study on the optical transitions in AlyInxGa1-x-yN (0.01≤ x ≤ 0.023, 0.07 ≤ y ≤ 0.14) of variable thickness (20 – 100 nm) grown on GaN by metalorganic chemical vapor deposition (MOCVD). At 100 K, highest electron mobility has been obtained for samples with 40 nm thick AlInGaN epilayer and this is due to the contribution from the two-dimensional electron gas (2DEG) in the confined two dimensional potential well. In literature, such 2DEG phenomenon is not discussed for AlInGaN quaternary alloys. In our samples, we have clearly observed such effects from low-temperature PL spectroscopy for AlInGaN epilayer of thickness ≥ 40 nm. The PL peaks observed due to the interband transitions from 2DEG sub-bands to the valence band are in the range 3.55 – 3.68 eV for the sample with an epilayer thickness of 100 nm. Due to the composition pulling effect in this alloy, there is a higher incorporation of Al towards the surface for thicker AlInGaN epilayer, which generates a stronger piezoelectric field and a deeper triangular potential for electron confinement. This is evident from the observation of higher intensity ratio for 2DEG transition compared to band-edge transitions, I2DEG/IBE in sample with thicker AlInGaN epilayer at higher temperature. The intensity ratio, I2DEG/IBE however decreases subsequently for all the samples with further increase in temperature due to thermal excitation. INTRODUCTION The recent penetration of light emitting diodes and laser diodes based on the III-nitride into the near UV region has motivated the fabrication of solid states light emitting sources emitting deep in the UV region. [1] Heterostructure with high aluminum content AlGaN encountered considerable strain induced defects such as cracks and stacking fault. AlyInxGa1-x-yN quaternary alloy has since been introduced to facilitate the lattice matching of the layers. [2] As the lattice constant and the band gap of AlInGaN quaternary alloy can be tailored independently, the concentration of the two dimensional electron gas in AlInGaN/GaN can be varied significantly when compared to that of the AlGaN/GaN heterostructure. Understanding the origin on the formation of 2DEG in AlInGaN/GaN is essential for the research on the feasibility of AlInGaN/ GaN based HFET. Studies have been carried out on factors influencing the density and mobility of carriers in AlInGaN/GaN based interface [3-4], effect of spontaneous and piezoelectric field on charge formation [5-6], donor attributed by surface states [7] and impurities in AlGaN layer. However, the
Data Loading...
