Dislocation Etch Pits in GaN Epitaxial Layers Grown on Sapphire Substrates

Abstract

Dislocations in GaN epitaxial layers grown on sapphire substrates have been studied by chemical etching. We have examined molten KOH as a defect etchant and characterized the etch pits on GaN layers. By use of molten KOH etching, etch pits were revealed on the surface of the GaN layer. All pits were hexagonal pyramids, which reflect the crystal symmetry of GaN. Results showed that molten KOH etching might be a useful method for the evaluation of the dislocations in GaN layers. The etch pit density (EPD) was typically 2 x i0 cm2.

Orthodox etching of HVPE-grown GaN

“…Among these methods the latter is the most attractive because it offers the possibility of establishing not only the one-to-one correspondence between the etch features and the individual defects but also to establish a correlation between different features and their causative defects. As a result TEM, has been the main technique used for calibration of recently developed defect-selective etching methods for GaN [9][10][11]. Two approaches are usually employed for this purpose, namely (i) comparison of dislocation density established by TEM with the density of etch pits (etch features), e.g.…”

“…Two approaches are usually employed for this purpose, namely (i) comparison of dislocation density established by TEM with the density of etch pits (etch features), e.g. [9] and (ii) examination of thin foils prepared from the etched samples using either conventional cross-section specimens [6,10] or focus ion beam (FIB) [12]. For calibration of the orthodox etching method, which reveals dislocations in the form of pits, the latter approach is the most favorable because it yields a direct association of the etch feature with the underlying defect.…”

“…TEM was most frequently used for calibration of different etching methods recently developed for revealing dislocations in GaN [4,[6][7][8][9][10][11][12]. As a rule orthodox etching in molten salts (KOH [9], eutectic alloy of KOH-NaOH=E etch [11] and E+MgO=E+M etch [13]) and hot acids [11,14] results in formation of pits of different sizes.…”

“…As a rule orthodox etching in molten salts (KOH [9], eutectic alloy of KOH-NaOH=E etch [11] and E+MgO=E+M etch [13]) and hot acids [11,14] results in formation of pits of different sizes. The attempts to attribute the size of pits to the type of dislocations showed unambiguously that the largest pits are formed on nano-pipes, i.e.…”

Fabrication of Smooth GaN-Based Laser Facets

“…This first step is required because the c-plane {0001} is impervious to all chemical agents investigated, 12,13 except at defect sites where etch pits occur. 14,15 In the second step the semiconductor sample is immersed in a hot chemical etchant that is able to crystallographically etch GaN. This etching step can produce smooth crystallographic surfaces, and the resulting etching planes are controlled by varying the orientation of the first step and the chemical agents and temperature of the second step.…”