Recognition and mapping of microdefects by photoetching, laser-scattering tomography and photoluminescence in SI undoped GaAs after different ingot-annealing treatments

Abstract

Three independent but complementary methods (OSL photoetching combined with etch rate profiling, spatially resolved PL and LST) were employed to Study the distribution of microdefects and electrically active centres in commercially available SI undoped. LEc-grown GaAs after different ingot-annealing treatments. A one-to-one correlation was obtained on comparing the microscale distribution of decoration precipitates (OPS), matrix precipitates (MPI) and microdefects (MMS) by the DSL and LST methods. Clustering of MPS is also revealed by PL intensity profiling and photoetch rate measurements. Two types of matrix microdefects are distinguishable by OSL photoetchlng In Samples after two-stage annealing. A high degree of homogeneity across the dislocation cells (after low-temperature and multiple annealing) was clearly revealed by a drastic decrease in the uniformity parameter (U) after DSL photoetching and by a significant decrease in the x intensity measured at the cell walls with respect to the cell interiors. Using the present results and recent data from the literature, an explanation of phase transitions during ingot annealing is proposed. This is based on the assumption that the final properties and structures after annealing are the result of two competitive processes: (i) formation of decoration and matrix microdefects; (ii) generation of electrically active point defects (clusters), presumably EL2

DSL Photoetching: Principles and Application to Study Nature of Defects in III-V Materials

“…7 the spheroids of the MP were present, therefore the etch rate increased in the shell of the spheroids but not in the centre. Such 3D distribution of the MP has been well-documented by previous studies using spatial Laser Scattering Tomography procedure [26,40].…”

“…At the same time a very high degree of chemical inhomogeneity in a microscale (across the dislocation cell walls) was observed in this type of GaAs [14,[24][25][26]. This effect is demonstrated by surface profiling on samples after the DSL photoetching (Fig.…”

“…It is known that the homogenization of GaAs is a consequence of two competitive diffusive processes that occur during annealing, namely (a) formation of As precipitates on dislocations (DP) and in the matrix (MP) and (b) formation of deep donor EL2 defects [29,[37][38][39]. It was also demonstrated that DSL photoetching combined with local etch rate measurements is an ultra-sensitive tool for recognizing these subtle structural changes [26]. Figure 7 demonstrates that both precipitates (DP, MP) and changes in the distribution of deep recombinative 1evels are clearly revealed by photoetching.…”

Dislocation cell structures in melt‐grown semiconductor compound crystals

“…As a result a lamellar-like structure with longitudinally extended walls is formed. There are some authors ascribing dislocation cell patterns in semiconductor compounds exclusively to such morphological instable interface [22,23]. However, as we clarified by depth integrating laser scattering tomography (LST) in GaAs [24] the dislocation cells are of globular type that contradicts longitudinal formed ones to be expected at cellular-shaped crystallization front.…”

Structural and electrical characteristics of undoped LEC GaAs crystals grown from slightly Ga-rich melts: a new approach

“…A surface profile from Figure 6c is typical of all S.I. undoped and In-doped GaAs crystals grown from As-rich melts examined up to now [13,18,20,21]. The presence of numerous, large (up to 200 nm) As decoration precipitates together with the photoetching behavior indicates that zone A of the ingots examined crystallized along the solidus line situated on the As-rich part of the Ga-As phase diagram, which implies the position of the congruent point also on the As side.…”