Chemically assisted ion beam etching of laser diode facets on nonpolar and semipolar orientations of GaN

Abstract

We demonstrate a vertical (<1°departure) and smooth (2.0 nm root mean square line-edge roughness (LER)) etch by chemically assisted Ar ion beam etching (CAIBE) in Cl 2 chemistry that is suitable for forming laser diode (LD) facets on nonpolar and semipolar oriented III-nitride devices. The etch profiles were achieved with photoresist masks and optimized CAIBE chamber conditions including the platen tilt angle and Cl 2 flow rate. Co-loaded studies showed similar etch rates of ∼60 nm min −1 for 2021 , 2021 , ( ¯¯) ( ¯) and m-plane orientations. The etched surfaces of LD facets on these orientations are chemically dissimilar (Ga-rich versus N-rich), but were visually indistinguishable, thus confirming the negligible orientation dependence of the etch. Continuous-wave blue LDs were fabricated on the semipolar 2021 ( ¯¯) plane to compare CAIBE and reactive ion etch (RIE) facet processes. The CAIBE process resulted in LDs with lower threshold current densities due to reduced parasitic mirror loss compared with the RIE process. The LER, degree of verticality, and model of the 1D vertical laser mode were used to calculate a maximum uncoated facet reflection of 17% (94% of the nominal) for the CAIBE facet. The results demonstrate the suitability of CAIBE for forming high quality facets for high performance nonpolar and semipolar III-N LDs.

Three-dimensional Characteristics of the Photonic Quantum Ring Laser

“…A significant reduction between the older device and the recent device for an offset value of 30 to 9.2 μm is noteworthy. In order to manufacture a PQR device, a mesa using a chemically assisted ion beam etching technology is formed [12]. Previously, the process conditions were not perfect, and the side surfaces of the device were rough.…”

Dynamic characteristics of 410 nm semipolar (202¯1¯) III-nitride laser diodes with a modulation bandwidth of over 5 GHz

“…An injection efficiency of 80% was extracted by analyzing the dependence of differential efficiency on cavity length for a number of different LDs, which is in a good agreement with the data reported by Becerra et al 11 The internal loss was estimated to be 16.9 cm À1 by considering the lowered reflectivity of the RIE-etched facet. 30 The lasing wavelength was around 410 nm, as shown in Fig. 2(b).…”

Semipolar {202¯1} GaN Edge-Emitting Laser Diode on Epitaxial Lateral Overgrown Wing

“…The slope efficiency was quite low, and we attribute this to strong scattering loss at the facets due to the imperfect RIE etching. We believe further improvements in the growth conditions, as well as the optimization of experimental structure, doping, inclusion of tunnel junctions [33], chemical treatments [34], vertical mirror facet formation [35] and bonding will lead to better L-I-V characteristics. In the past, researchers reported nearly vertical facet formation in the semipolar LDs by Cl 2 gas/Ar-ion chemically assisted ion beam etching (CAIBE) in an Oxford Ion Mill system [35]; as a result, our future investigations will include this method for on-wafer facet formation.…”