Distributions of residual stress, dislocations, and EL2 in Czochralski-grown semi-insulating GaAs

Abstract

Distributions of stress, dislocations, and the EL2 midgap defect have been optically mapped in semi-insulating GaAs wafers, from [100]-grown crystals created by the liquid-encapsulated Czochralski method. The evolution of EL2 along the growth axis indicates that assessment of this property through the majority of the crystal volume is often poorly represented by wafers from near the two end regions. A comparison of maps for stress, dislocation and EL2 patterns as all measured with a given wafer does not support hypotheses that EL2 is a direct consequence either of stress or of dislocations. Other mechanisms, such as segregation and melt dynamics, thus appear more likely to control the formation and distribution of EL2.

Infra-red imaging and EL2

“…based on the relative importance of the scattered light [23]. Then the point is the understanding of the mechanism of EL2 generation or gettering by dislocations [66]. Alternative models were also proposed by Bray [36] and Weber [7] using the balanced equilibrium with an acceptor.…”

“…Another interesting discussion in the field was proposed by Dobrilla [66] ; supposing that EL2 is generated in the close vicinity of dislocations, the high EL2 density regions would correspond to small cell regions (high EPD) whereas if EL2 is generated independently from dislocations the cell modulation would be superimposed on a background evolution. The situation is depicted in figure 8.…”

EL2 distribution in LEC GaAs ingots and wafers

“…In order to have a better understanding of this effect, we have analysed the distribution of EL2 center in the undoped semiinsulating ingots, grown in our laboratory, by using a combination of Hall effect and optical absorption measurements on a two-inch wafer [13]. The distribution of EL2 has also been measured with optical [18][19][20], or electrical experiments [21]. 2.…”