Jul 29, 2016

Piezoelectric field in highly stressed GaN-based LED on Si (1 1 1) substrate

Highlights

Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire were measured.
Large tensile stress is observed in GaN epilayers grown on Si (1 1 1).
The piezoelectric field in the MQW region was monitored using ER spectroscopic method.
The large tensile stress with Si (1 1 1) substrate is regarded as external stress.
External tensile stress compensates for the compressive stress developed in the MQW.

Abstract

Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire, and their effects on built-in piezoelectric field induced by compressive stress in InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) were investigated using the electroreflectance (ER) spectroscopic technique. Relatively large tensile stress is observed in GaN epilayers grown on Si (1 1 1), while a small compressive stress appears in the film grown on c-plane sapphire. The InGaN/GaN MQWs of LED on c-plane sapphire substrate has a higher piezoelectric field than the MQWs of LEDs on Si (1 1 1) substrate by about 1.04 MV/cm. The large tensile stress due to lattice mismatch with Si (1 1 1) substrate is regarded as external stress. The external tensile stress from the Si substrate effectively compensates for the compressive stress developed in the active region of the InGaN/GaN MQWs, thus reducing the quantum-confined Stark effect (QCSE) by attenuating the piezoelectric polarization from the InGaN layer.

Keywords

  • Silicon substrate
  • Piezoelectric field
  • ER spectroscopic technique
      • Source: Sciencedirect
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