GaN-Based High Power Blue-Violet Laser Diodes

Abstract

The epitaxial lateral overgrowth (ELO) technique is an important technology for improving the characteristics of GaN-based laser diodes (LDs). The photoluminescence intensities from GaN and GaInN multiple quantum well active layers in the ELO-GaN wing region were found to be higher than those in the seed region. This indicates that the density of dislocations in the wing region could be reduced significantly. This is evidenced by dislocation densities of less than 106 cm-2 as determined from transmission emission microscopy and etching-pit-density measurements. The cleaved facets of LDs on ELO-GaN and sapphire were observed by atomic forced microscopy. Although the roughness of GaN cleaved facets on sapphire were high (Ra>10 nm), the roughness in the ELO-GaN wing region was found to be as smooth as that of GaAs cleaved facet (Ra<1 nm). The characteristics of LDs on ELO-GaN were found to be superior to those on sapphire as a result of smoother facets and lower dislocation densities.

Carrier Transport Phenomena in Metal Contacts to AlInGaN-Based Laser Diodes

“…As the measured temperature decreased, as shown in Fig. 9, the contact resistivity of the Pd/Pt/Au contacts 20 cm -3 , the contact resistivity increased from 5.5x10 -4 to 4.0x10 -2 Ω-cm 2 , as the temperature decreased from 300 to 100 K. In case of the contacts on the sample A or B, the contact resistivity also increased by more than one order of magnitude as the temperature decreased from 300 to 100 K. These results clearly show that the carrier transport at the Pd/p-GaN interface is not dominated by pure-tunneling mechanism because it implies a temperature-independent contact resistance. [15] It is worthwhile to note that the contact resistivity of the non-alloyed Pd/Pt/Au contacts on the sample C (5.5x10 -4 Ω-cm 2 ) having a low hole concentration of 2.0x10 16 cm -3 was anomalously low at room temperature, considering the large work function difference between Pd and p-GaN.…”

“…As shown in Fig. 1, the [Mg] increased with Cp 2 Mg and reached up to 1x10 20 cm -3 when the flow rate of Cp 2 Mg was 2.8 μmole/min. The hole concentration initially increased from 7.5x10 16 (sample A) to 2.2x10 17 cm -3 (sample B) with the increase of the flow rate of Cp 2 Mg from 0.70 to 1.05 μmole/min.…”

“…[17,18] Indeed, the use of LEO GaN has already increased the lifetime of InGaN LDs to more than 10,000 hours. [19,20] The electrical characteristics of dislocations in n-GaN have been well studied. Weimann et al suggested a model in which filled traps along dislocation lines act as Coulomb scattering centers, explaining the low transverse mobility in GaN by the scattering of electrons at charged dislocation lines.…”

“…In addition, the effect of dislocation density on threshold current and life time of InGaN LDs were reported in several papers, [19,20,25] while, little results on the effects of dislocation density on the operating voltage of the InGaN LDs have been reported until now. Nam et al reported that the lifetime of the InGaN LDs was greatly influenced by the operating voltage, although it is well known that the lifetime is affected by the operation current and the temperature of the LDs.…”

“…One of the main concerns in this area is the fabrication of high-quality ohmic contacts to p-GaN with low resistance and thermal stability, since operation power of the AlInGaN-based LDs greatly affects the life time of the LDs. [1] Achieving low resistance ohmic contacts to p-GaN has been particularly challenging, because of difficulty in obtaining a hole concentration over 10 18 cm -3 and the absence of metals having a work function higher than that of p-GaN (6.5 eV). [2] For fabrication of AlInGaN-based LDs with low input power, free-standing GaN has attracted attention as a substrate because of its low dislocation density, high thermal conductivity, and easy cleaving.…”