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Observation of dislocations in GaAs epitaxial layers
Journal of Crystal Growth 52 (1981) 925—928 © North-Holland Publishing Company
OBSERVATION OF DISLOCATIONS IN GaAs EPITAXIAL LAYERS J. NISHIZAWA, Y. OYAMA and Y. OKUNO* Research Institute of Electrical Communication, Tohoku University, Sendai 980, Japan
Dislocations in GaAs epitaxial layers grown by the temperature difference method of liquid phase epitaxy were observed using X-ray topography and a chemical etching technique. Dislocations in the substrates seem to react with those propagating along the two orthogonal (110) directions at the interface. The propagation of dislocations from the substrates into the epitaxial layers and the interface lattice distortion of the GaAs homojunctions were investigated using X-ray topography of cleavage surfaces.
1. Introduction
order to investigate the behavior of dislocations in the growth direction, a step etching technique was used.
Dislocations in GaAs crystals have been widely investigated by means of etching [1], Xray topography [2] and transmission electron microscopy [3]. Authors observed dislocations along the (110) directions at the interface by means of a new chemical etchant called “modified super oxidiser” (MSO) [4]. In this paper we report results on dislocations along the (110) direction obtained by X-ray topography and a chemical etching technique.
3. Results and discussion Fig. I shows an anomalous transmission X-ray topography of the GaAs specimen grown in a {001} oriented substrate. This reveals the dislocations propagating along the two orthogonal (110) directions. In order to determine the Burgers vector of these dislocations, transmission X-ray topographs were taken using various kinds of diffraction plane. (220) diffraction reveals these dislocations while (220) and (111) diffraction give no image. So these dislocations have the Burgers vector shown in fig. 2. Reflection X-ray topograph gives no dislocation image. And after removal of the epitaxial layer, these dislocations cannot be seen by X-ray diffraction topography. After repetition of stain etching, MSO etchant reveals these dislocations propagating along the two orthogonal (110) directions near the interface between substrate and epitaxial layer. So these dislocations exist in the interface region. Fig. 3 shows the stain etched pattern corresponding to the dislocations lying along the (110) direction near the interface. These (110) dislocations seem to react with those in the substrate. And some dislocations in the substrates are expected to bend at the interface and do not propagate into the epitaxial layers.
2. Experiments The specimens were undoped GaAs grown by the temperature difference method of liquid phase epitaxy [5] on {001} oriented Si-doped or Cr-doped substrates. The etch pit density of substrates is 5 x 10~to 10~cm2. The typical carrier concentration and Hall mobility of the epitaxial layers at 77 K are 1 x 1014 cm3 and 7 X 10~cm2 V~s~ respectively. Dislocations in the GaAs crystals were observed by X-ray topography and a chemical etching technique. MSO etchant can reveal dislocations with an etching depth less than I j.tm. The surface morphology was observed using a Reichert optical microscope with Nomarski interference contrast. In *
Semiconductor Research Institute, Kawauchi, Sendai 980. Japan. 925
926
J. Nishizawa et al. I Dislocations in GaAs epitaxial layers
Fig. 3. Dislocations along (110) direction revealed by the MSO etchant at the interface. They seem to react with those in the substrate.
Fig. I. Anomalous transmission X-ray topograph of undoped GaAs epitaxial layer grown on the {001} onented Cr-doped substrate. This reveals dislocations propagating along the two orthogonal (110) directions,
~
______________________
(110) ,‘.O
DIRECTION OF DISLOCATION
BURGERS VECTOR OF <110>
DISLOCATION
Fig 2 Schematic diagram of the Burgers vector of dislocations along (110) direction.
We observed dislocations on the cleavage surface revealed by the MSO etchant. Fig. 4 shows the etch pattern corresponding to dislocations. To determine the slip plane of these dislocations, transmission and reflection X-ray topographs
were taken by using various kinds of diffraction plane. (111) diffraction shows no dislocation images in the epitaxial layer, but reveals dislocations in the substrate. On the contrary (III) diffraction shows no dislocation images in the substrate but reveals dislocations in the epitaxial layer. If the most close packed {11l} plane is the slip plane, dislocations in the epitaxial layer and the substrate have different slip planes. The dislocations in the substrate seem to dissociate at the interface and propagate into the epitaxial layer as shown in fig. 5. X-ray topographs of the cleavage surface reveal dislocation images in the substrate which seem to bend at the interface and do not propagate into the epitaxial layer. And X-ray topographs of the cleavage surface reveal dislocation images introduced from the crystal surface. The step etching technique and transmission X-ray topographs after repetitive step etching also reveal these dislocations intro.
.
.
.
.
duced the crystal surface. locationsfrom introduced from the crystal These surface disare thought to be dislocation loops including paired loops, because dislocations cannot end in the crystal. The propagation of dislocations from the substrate into the epitaxial layer is shown in fig. 5. The characteristics of the interface and the quality of epitaxial layer are expected to affect the behaviour of propagation of dislocations
J. Nishizawa et a!. / Dislocations in GaAs epitaxial layers
927
~ INTERFACE
Fig. 4. Dislocations on the cleavage surface revealed by the MSO etchant. Dislocations in the substrate seem to propagate into the epitaxial layer. C
EPITAXIAL
/
/
EPITAXIAL LAYER
A/’
____________
LAYER
INTERFACE
__________________
SUBSTRATE
______
INTERFACE SUBSTRATE
______
AB
C
// /1 J
\1\!
I7 /
1
/ ~J E
—
~
D
- —
I/~‘~I/
/ ]
/ I
EPITAXIAL LAYER F
INTERFACE
(110) SPACING Fig. 6. Schematic diagram of the lattice distortion near the
SUBSTRTE
interface revealed by the X-ray topographic method.
b
Fig. 5. (a) Schematic diagram of the propagation of dislocations observed on the cleavage surface. (b) Schematic diagram of the propagation of dislocations from the substrate into the epitaxial layer.
from the substrate into the epitaxial layer. We investigated the interface lattice distortion by using X-ray topography [5]. Reflection and transmission X-ray topographs were taken for various diffraction planes (111) and (004) diffraction, which are included and parallel to the crys-
tal surface respectively, reveal an interface image. But (220) diffraction, which is perpendicular to the crystal surface, shows no interface image. So the lattice distortion in the interface region is expected to be shown as schematically in fig. 6. .
.
.
.
4. Conclusion Dislocations in the (110) directions exist at the interface of GaAs homojunctions and have a Burgers vector as shown in fig. 2. They seem to interact with those in the substrate. In other
9~
J. Nishizawa et al. / Dislocations in GaAs epitaxial layers
words, some dislocations in the substrates seem to bend at the interface and do not propagate into the epitaxial layers. Some dislocations in the epitaxial layers seem to be introduced from the crystal surface. Lattice distortion in the interfacial region was investigated by X-ray topography. Propagation of dislocations from the substrate into the epitaxial layer is thought to be affected by the properties of the epitaxial layers, especially the density of the point defects in the epitaxial layers. Further study of the propagation of dislocations is being continued.
References ~
MS. Abrahams and C.J. Buiocchi, J. App!. Phys. 36
(1965) 2855. [2] W.J. Bartels and W. Nijman, J. Crystal Growth 37 (1977) 204. [3] G.H. Olsen, J. Crystal Growth 31(1975) 223. [4] J. Nishizawa, Y. Oyama, H. Tadano, K. Inokuchi and Y. Okuno, J. Crystal Growth 47 (1979) 434. [5] J. Nishizawa and Y. Okuno, IEEE Trans. Electron Devices ED-22 (1975) 716. [6] S. Kishino and S. lida, J. Electrochem. Soc. 119 (1972) 1113
OBSERVATION OF DISLOCATIONS IN GaAs EPITAXIAL LAYERS J. NISHIZAWA, Y. OYAMA and Y. OKUNO* Research Institute of Electrical Communication, Tohoku University, Sendai 980, Japan
Dislocations in GaAs epitaxial layers grown by the temperature difference method of liquid phase epitaxy were observed using X-ray topography and a chemical etching technique. Dislocations in the substrates seem to react with those propagating along the two orthogonal (110) directions at the interface. The propagation of dislocations from the substrates into the epitaxial layers and the interface lattice distortion of the GaAs homojunctions were investigated using X-ray topography of cleavage surfaces.
1. Introduction
order to investigate the behavior of dislocations in the growth direction, a step etching technique was used.
Dislocations in GaAs crystals have been widely investigated by means of etching [1], Xray topography [2] and transmission electron microscopy [3]. Authors observed dislocations along the (110) directions at the interface by means of a new chemical etchant called “modified super oxidiser” (MSO) [4]. In this paper we report results on dislocations along the (110) direction obtained by X-ray topography and a chemical etching technique.
3. Results and discussion Fig. I shows an anomalous transmission X-ray topography of the GaAs specimen grown in a {001} oriented substrate. This reveals the dislocations propagating along the two orthogonal (110) directions. In order to determine the Burgers vector of these dislocations, transmission X-ray topographs were taken using various kinds of diffraction plane. (220) diffraction reveals these dislocations while (220) and (111) diffraction give no image. So these dislocations have the Burgers vector shown in fig. 2. Reflection X-ray topograph gives no dislocation image. And after removal of the epitaxial layer, these dislocations cannot be seen by X-ray diffraction topography. After repetition of stain etching, MSO etchant reveals these dislocations propagating along the two orthogonal (110) directions near the interface between substrate and epitaxial layer. So these dislocations exist in the interface region. Fig. 3 shows the stain etched pattern corresponding to the dislocations lying along the (110) direction near the interface. These (110) dislocations seem to react with those in the substrate. And some dislocations in the substrates are expected to bend at the interface and do not propagate into the epitaxial layers.
2. Experiments The specimens were undoped GaAs grown by the temperature difference method of liquid phase epitaxy [5] on {001} oriented Si-doped or Cr-doped substrates. The etch pit density of substrates is 5 x 10~to 10~cm2. The typical carrier concentration and Hall mobility of the epitaxial layers at 77 K are 1 x 1014 cm3 and 7 X 10~cm2 V~s~ respectively. Dislocations in the GaAs crystals were observed by X-ray topography and a chemical etching technique. MSO etchant can reveal dislocations with an etching depth less than I j.tm. The surface morphology was observed using a Reichert optical microscope with Nomarski interference contrast. In *
Semiconductor Research Institute, Kawauchi, Sendai 980. Japan. 925
926
J. Nishizawa et al. I Dislocations in GaAs epitaxial layers
Fig. 3. Dislocations along (110) direction revealed by the MSO etchant at the interface. They seem to react with those in the substrate.
Fig. I. Anomalous transmission X-ray topograph of undoped GaAs epitaxial layer grown on the {001} onented Cr-doped substrate. This reveals dislocations propagating along the two orthogonal (110) directions,
~
______________________
(110) ,‘.O
DIRECTION OF DISLOCATION
BURGERS VECTOR OF <110>
DISLOCATION
Fig 2 Schematic diagram of the Burgers vector of dislocations along (110) direction.
We observed dislocations on the cleavage surface revealed by the MSO etchant. Fig. 4 shows the etch pattern corresponding to dislocations. To determine the slip plane of these dislocations, transmission and reflection X-ray topographs
were taken by using various kinds of diffraction plane. (111) diffraction shows no dislocation images in the epitaxial layer, but reveals dislocations in the substrate. On the contrary (III) diffraction shows no dislocation images in the substrate but reveals dislocations in the epitaxial layer. If the most close packed {11l} plane is the slip plane, dislocations in the epitaxial layer and the substrate have different slip planes. The dislocations in the substrate seem to dissociate at the interface and propagate into the epitaxial layer as shown in fig. 5. X-ray topographs of the cleavage surface reveal dislocation images in the substrate which seem to bend at the interface and do not propagate into the epitaxial layer. And X-ray topographs of the cleavage surface reveal dislocation images introduced from the crystal surface. The step etching technique and transmission X-ray topographs after repetitive step etching also reveal these dislocations intro.
.
.
.
.
duced the crystal surface. locationsfrom introduced from the crystal These surface disare thought to be dislocation loops including paired loops, because dislocations cannot end in the crystal. The propagation of dislocations from the substrate into the epitaxial layer is shown in fig. 5. The characteristics of the interface and the quality of epitaxial layer are expected to affect the behaviour of propagation of dislocations
J. Nishizawa et a!. / Dislocations in GaAs epitaxial layers
927
~ INTERFACE
Fig. 4. Dislocations on the cleavage surface revealed by the MSO etchant. Dislocations in the substrate seem to propagate into the epitaxial layer. C
EPITAXIAL
/
/
EPITAXIAL LAYER
A/’
____________
LAYER
INTERFACE
__________________
SUBSTRATE
______
INTERFACE SUBSTRATE
______
AB
C
// /1 J
\1\!
I7 /
1
/ ~J E
—
~
D
- —
I/~‘~I/
/ ]
/ I
EPITAXIAL LAYER F
INTERFACE
(110) SPACING Fig. 6. Schematic diagram of the lattice distortion near the
SUBSTRTE
interface revealed by the X-ray topographic method.
b
Fig. 5. (a) Schematic diagram of the propagation of dislocations observed on the cleavage surface. (b) Schematic diagram of the propagation of dislocations from the substrate into the epitaxial layer.
from the substrate into the epitaxial layer. We investigated the interface lattice distortion by using X-ray topography [5]. Reflection and transmission X-ray topographs were taken for various diffraction planes (111) and (004) diffraction, which are included and parallel to the crys-
tal surface respectively, reveal an interface image. But (220) diffraction, which is perpendicular to the crystal surface, shows no interface image. So the lattice distortion in the interface region is expected to be shown as schematically in fig. 6. .
.
.
.
4. Conclusion Dislocations in the (110) directions exist at the interface of GaAs homojunctions and have a Burgers vector as shown in fig. 2. They seem to interact with those in the substrate. In other
9~
J. Nishizawa et al. / Dislocations in GaAs epitaxial layers
words, some dislocations in the substrates seem to bend at the interface and do not propagate into the epitaxial layers. Some dislocations in the epitaxial layers seem to be introduced from the crystal surface. Lattice distortion in the interfacial region was investigated by X-ray topography. Propagation of dislocations from the substrate into the epitaxial layer is thought to be affected by the properties of the epitaxial layers, especially the density of the point defects in the epitaxial layers. Further study of the propagation of dislocations is being continued.
References ~
MS. Abrahams and C.J. Buiocchi, J. App!. Phys. 36
(1965) 2855. [2] W.J. Bartels and W. Nijman, J. Crystal Growth 37 (1977) 204. [3] G.H. Olsen, J. Crystal Growth 31(1975) 223. [4] J. Nishizawa, Y. Oyama, H. Tadano, K. Inokuchi and Y. Okuno, J. Crystal Growth 47 (1979) 434. [5] J. Nishizawa and Y. Okuno, IEEE Trans. Electron Devices ED-22 (1975) 716. [6] S. Kishino and S. lida, J. Electrochem. Soc. 119 (1972) 1113