Reduction of Internal Loss and Threshold Current in a Laser Diode with a Ridge by Selective Re-Growth (RiS-LD)

Abstract

The origin of the internal loss in ridge‐type laser diodes (LDs) fabricated using selective re‐growth is investigated through a systematic device characterization and additional optical measurements. We found that the internal loss of this LD is mainly caused by the absorptive layers at the re‐growth boundary and Mg‐doped GaN layer. The internal loss can be significantly reduced through a re‐design of the LD structure to avoid these absorptive regions by shifting the perpendicular optical field to the n‐cladding side. The re‐designed LDs had a very low threshold current of 10 mA and superior gain characteristics. These results indicate, that the InGaN‐quantum‐well (QW) active layer has a large differential gain and fewer non‐radiative defects. The fabrication method of this LD, i.e. epitaxial growth on low‐dislocation‐density GaN substrates combined with a process without dry‐etching, is responsible for the high quality of the QWs.

Improvement of characteristics of InGaN-based laser diodes with undoped InGaN upper waveguide layer

“…In the InGaN-based laser diodes, the absorption coefficients near the wavelength of 400 nm of Mg-doped p-type GaN, Sidoped n-type GaN, and undoped GaN layers are 100 cm À1 , 30 cm À1 , and 10 cm À1 , respectively. 13,14 The absorption coefficients of AlGaN and InGaN layers are assumed to be similar to GaN when Al or In composition is relatively low. The optical absorption loss of InGaN-based laser diodes is mainly produced in the region of p-type waveguide layer and p-type AlGaN cladding layer.…”

AlGaN-Based Vertical Injection Laser Diodes Using Inverse Tapered p-Waveguide for Efficient Hole Transport

“…Except for the QWs, the entire epitaxial structure of Table I is assumed to be optically transparent at the emission wavelength (290 nm). We address the influence of optical loss associated with sub-bandgap absorption [24] at the end of Section III, and stress that the asymmetric waveguide design presented in Table I minimizes such deleterious effects by pushing the optical mode towards less lossy n-type layers [25], [26].…”

Design Considerations for GaN-Based Blue Laser Diodes With InGaN Upper Waveguide Layer

“…The data of the refractive index are taken the same as those reported in the previous studies [10]. In addition, the absorption coefficients of Mg-doped, Si-doped, and undoped GaN are taken as 100, 30, and 10 cm −1 , respectively [11]. For AlGaN and InGaN, the absorption coefficients are approximated taken to be the same as GaN.…”