Milliwatt‐class GaN‐based blue vertical‐cavity surface‐emitting lasers fabricated by epitaxial lateral overgrowth

Abstract

We have achieved continuous‐wave (CW) operation of gallium nitride (GaN)‐based vertical‐cavity surface‐emitting lasers (VCSELs) fabricated by epitaxial lateral overgrowth (ELO) using dielectric distributed Bragg reflectors (DBRs) as masks for selective growth. The GaN VCSELs exhibited CW operation at a wavelength of 453.9 nm, and the maximum output power was 1.1 mW, which is the highest value reported to date. GaN‐based materials have presented challenges for obtaining DBRs with high reflectivity and a wide stopband, precise control of the cavity length and a lateral confinement structure to provide laser operation. The proposed VCSEL is immune to these concerns. Its two dielectric DBRs were obtained free from cracks. A high reflectance of more than 99.9% and a stopband with a width of 80–97 nm were obtained for both DBRs. The cavity length was controlled by epitaxial growth to as short as 4.5 µm. An ITO contact electrode on p‐type GaN, which is required for a lateral confinement structure, showed electrical reliability under a high current density of 59.6 kA cm−2. The present data demonstrate that the fabrication process adopted here overcomes the shortcomings that have prevented the widespread use of GaN‐based VCSELs.

A GaN‐Based VCSEL with a Convex Structure for Optical Guiding

“…[14] At the same time, the value of the maximum LOP with the convex structure here was 0.88 mW, which is somewhat lower than those of the state-of-the-art GaN-VCSELs. [1][2][3][4] Further investigations and optimizations are necessary. Figure 5(a) and (b) show emission spectra and corresponding NFPs of the GaN-based VCSELs with and with-out the convex structure.…”

“…Recently developments of GaNbased VCSELs emitting 400-450 nm light have been intensively carried out, showing maximum light output power (LOP) values of 1 mW and more. [1][2][3][4] Also, reasonably low threshold currents, a few mA, of GaN-based VCSELs have been reported. [1,[5][6][7] However, external differential quantum efficiencies (η d ) of the GaN-based VCSELs are still much lower (%10%) than those of red/infrared VCSELs (30-60%).…”

Progress and challenges in electrically pumped GaN-based VCSELs

“…Publications from a few groups followed, and since the first demonstrations there have been a lot of progress in the field of electrically injected III-nitride based VCSELs, both in terms of new technological solutions as well as performance characteristics. 31 To date there are seven groups in the world who have demonstrated lasing under electrical injection [27][28][29][30][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] , and the different approaches and structures are summarized in Table 1. The performance characteristics of published devices, in terms of output power and threshold current density, are plotted in Fig.…”

“…In GaAs-VCSELs simultaneous current and optical confinement is achieved by selective oxidation of a high Al-content AlGaAs-layer. Recently, new approaches for current confinement in GaN-VCSELs have been developed such as plasma damage of p-GaN 32 , ion implantation 36,47 , and airgaps by photoelectrochemical etching 38 . A number of key challenges in GaN-VCSEL will be described in more detail in the next chapter.…”

A Study of the Photoelectrochemical Etching of n-GaN in H3PO4 and KOH Electrolytes

“…There has also been remarkable progress in the development of GaN-based laser diodes (LDs) and in particular there has been considerable recent work on vertical-cavity surface-emitting lasers (VCSELs). [5][6][7][8] GaN is an attractive candidate material for high-voltage and high-power devices [9][10][11][12] because of its high electric field strength and electron mobility. It is also a promising semiconductor for solar energy conversion by photoelectrochemical water splitting or photovoltaic power gereration.…”