Charge separation due to spontaneous and piezoelectric polarization inherent to the wurtzite structure has deleterious effects on the performance of most c-axis oriented devices.1) To overcome this problem, Nonpolar GaN, such as a-plain and m-plain GaN or Semipolar GaN substrates have been grown.
We reported the fabrication of violet InGaN/GaN Light Emitting Diodes (LEDs) on semipolar (1011) GaN bulk substrates. The output power and External Quantum Efficiency (EQE) at a driving current of 20 mA were 28 mW and 45 % respectively, with peak electroluminescence (EL) emission wavelength at 411 nm. The LEDs showed minimal shift in peak EL wavelength with increasing drive current indicating an absence of polarization induced electric fields.2) Also, high power and high efficiency nonpolar m-plane nitride LEDs were fabricated on low extended defect bulk m-plane GaN substrates.3) The first nonpolar m-plane (1100) nitride laser diodes (LDs) were realized on low extended defect bulk m-plane GaN substrates.4) Broad area lasers without AlGaN cladding layers were fabricated and tested under pulsed conditions. These laser diodes had threshold current densities (J_th) as low as 3.7-2.3 kA/cm².5) Stimulated emission was observed around 400 nm. The recent performance of Nonpolar, Semipolar and Polar (c-plain) GaN-based devices are described. Also, I like to talk about the latest result of a GaN bulk crystal growth by anmmothermal method at UCSB.

References

1. S. Chichibu, T. Azuhata, T. Sota, and S. Nakamura, Appl. Phys. Lett. 69, 4188 (1996)
2.A. Tyagi, H. Zhong, N. N. Fellows, M. Iza, J. S. Speck, S. P. DenBaars, and S.i Nakamura, Jpn. J. Appl. Phys. 46 (2007) L129
3.M. C. Schmidt, K-C Kim, H. Sato, N. Fellows, H. Masui, S. Nakamura, S. P. DenBaars, and J. S. Speck, Jpn. J. Appl. Phys. 46 (2007) L126
4.M.C. Schmidt, K-C Kim, R.M. Farrell, D. F. Feezell, D.l A. Cohen, M. Saito, K.Fujito, J. S. Speck, S.P. DenBaars, and S. Nakamura, Jpn. J. Appl. Phys. L190-L191, Vol 46 (2007).
5.D.F. Feezell, M.C. Schmidt, R. M. Farrell, K-CKim, M. Saito, K. Fujito, D.l A. Cohen, J. S. Speck, S.P. DenBaars, and S. Nakamura, Jpn. J. Appl. Phys. L284-L286, Vol 46 (2007).

1. Ammonothermal Growth of Bulk GaN for Extended Time
2. Characterization of chrystallographic properties and defects via X-ray microdiffraction in GaN(0001) layers
3. GaN Crystal Growth and Light Emitting Devices