Liu Junlin

Status of GaN-based green light-emitting diodes*

GaN-based blue light emitting diodes (LEDs) have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency (EQE) of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantum well (QW) with low strain. Many techniques of improving efficiency are discussed, such as inserting AlGaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported: high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.

High optical efficiency GaN based blue LED on silicon substrate

After nearly ten years of exploration, our team firstly had a breakthrough in the technologies of materials growth and thin film chip manufacturing for high efficiency GaN based blue LED on silicon substrate in the world. The internal quantum efficiency and extraction efficiency of the vertical structure blue LED chips reached 80%. These LED chips have been realized mass production, and been successfully used in street lamps, miners lamp, down light, bulb light, flashlight and display imaging etc. In this paper, the related key technologies are comprehensive and systematically introduced. Selective-Area-Growth and Maskless-Micro-Epitaxial-Lateral-Overgrowth technologies were invented, by which a high crystalline quality GaN film was achieved with an only 100 nm AlN buffer layer. A set of systemic technologies were invented for manufacturing vertical thin film structure LED on silicon substrate, included high reflectance low resistance P type ohmic contact electrode, high stability low resistance N type electrode ohmic contact, surface roughening, complementary electrode, releasing residual tensile stress of GaN film technologies etc. At 350 mA (35 A/cm2), the light output power of blue LED (450 nm) on silicon is 657 mW, and external quantum efficiency of it is 68.1%.

Effects of Carrier Gas on Carbon Incorporation in GaN

GaN epitaxial layers were grown on Si (111) substrates by metal organic chemical vapor deposition. Carbon concentrations in the films grown in different ambients were measured by secondary ion mass spectrometry. The results show that the carbon incorporation is strongly dependent on the H2 flow rate when the NH3 flow rate is small, but insensitive to the H2 flow rate when the NH3 flow rate is sufficient large. We conclude that H2 can inhibit the dissociation of NH3 and result in a less active N source; an insufficiently active N source causes more N vacancies, which enhances carbon incorporation.