Selective and controllable lateral photoelectrochemical etching of nonpolar and semipolar InGaN/GaN multiple quantum well active regions

Abstract

We demonstrate the selective and controllable undercut etching of the InGaN/GaN multiple quantum well active regions of nonpolar and semipolar laser diode (LD) structures by photoelectrochemical (PEC) etching without external bias. The lateral etch rate ranged from >20 nm/min to >1.2 µm/min. Metal masks were used to define the undercut and to improve the PEC etch resolution by reducing the scattered light in the system, which contributes to degradation of the lateral etch resolution, as suggested by ray tracing simulations. This resulted in a light-exposed-area: masked-area etch selectivity of 13 : 1.

Estimation of roughness-induced scattering losses in III-nitride laser diodes with a photoelectrochemically etched current aperture

“…Roughness values of the PEC etched active region edges were previously obtained by analysis of fluorescence optical microscope images . Although optical microscope images can provide very large dataset, which is necessary to have a good estimation of the parameters to be measured , they suffer from low resolution in analyzing very small features.…”

Microdisk-Type Multicolor Semipolar Nitride-Based Light-Emitting Diodes

“…This is because, in the wet-etching process, the semipolar GaN film is etched by a chemical etchant to avoid dry-etching damage . Recently, only a few reports are available on the wet-etching phenomena of nonpolar and semipolar GaN films that can yield higher emission efficiency because of the increase of LEE and control of the active region of the laser diode. , These wet-etching studies have been limited to the auxiliary process after the dry-etching or cleaving process to form the undercut and rough surface structures of the active layer in the light-emitting devices. − However, the wet-etching process will be a very useful alternative to the dry-etching process because it can reduce the etching damage and improve the emission efficiency as the size of semipolar InGaN-based full-color micro-LEDs is reduced . To the best of our knowledge, it is difficult to find studies using only the wet-etching process for the entire mesa structure, except for our previous report, because of the immature wet-etching technology of the semipolar LED fabrication process .…”

“…14 Recently, only a few reports are available on the wet-etching phenomena of nonpolar and semipolar GaN films that can yield higher emission efficiency because of the increase of LEE and control of the active region of the laser diode. 32,33 These wet-etching studies have been limited to the auxiliary process after the dry-etching or cleaving process to form the undercut and rough surface structures of the active layer in the light-emitting devices. 32−34 However, the wet-etching process will be a very useful alternative to the dryetching process because it can reduce the etching damage and improve the emission efficiency as the size of semipolar InGaN-based full-color micro-LEDs is reduced.…”

Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates

“…The etch rate is also crystallographically dependent [12]. Lateral etching of selectively excited III-nitride layers has been used to create deeply undercut structures grown on sapphire [13], to create undercut apertures in laser diode structures on bulk m-plane and semipolar (202 1) GaN substrates [14], to lift off verticalcavity surface-emitting lasers (VCSELs) from bulk m-plane GaN substrates [15,16], and to remove blue LEDs from bulk semipolar (202 1) GaN substrates [17].…”