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Etching study on CdSnP2 prismlike crystals
Journal ofCrystal Growth 51(1980)143 —146 © North-Holland Publishing Company
LETTER TO THE EDITORS ETCHING STUDY ON CdSnP2 PRISMLIKE CRYSTALS Takashi MATSUIMOTO and Tetsuro ISHIDA Department of Electronic Engineering, Yamanashi University, Takeda-4, Kofu 400, Japan Received 8 August 1980
Prismlike crystals of CdSnP2 grown from a tin solution were etched in a solution of 1 HF + 2 HNO3 + 2 H20. Characteristic etch figures were revealed on the (112), (112) and (101) facets. On the planes perpendicular to the (111) axis, etch pits and twin boundary lines were observed. Twin planes parallel to the {l 12} plane were found in many of the prismlike crystals.
Cadmium tin diphosphide (CdSnP2) is one of the chalcopyrite semiconductors, and considerable work has been done on its electronic structure and luminescent properties [1]. In order to use this material for electronic devices, device technology such as chemical etching is required. However, little has been reported on either etchants or etching properties of CdSnP2 crystals. In this letter, we describe the characteristics of etch figures observed on the facets of solution grown prismlike CdSnP2 crystals. Crystals of CdSnP 2 were grown from a tin solution by slow cooling [2,3]. A mixture of atomic composition of 33% Cd, 6.7% P and 90% Sn was sealed in an evacuated quartz ampoule at a pressure lower than iO~ Torr. The ampoule was heated to 800°C and held at this temperature for 28 h to homogenize the melt. The melt was slowly cooled at a rate of 5 K/h
I
_
from 600°C to 290°C according to the CdP2—Sn phase diagram [2]. The tin and the grown crystals were separated in hot glycerin at a temperature higher than the melting point of tin (232°C).Strain-free prismlike crystals were obtained by means of this technique. Residual tin attached to the grown crystals was removed by dissolution in a solution of 1 HF + 2 HNO3 + 2 1120. Crystals not intentionally doped were of n-type with resistivities of 0.01 0.03 &2 cm 3and electron concentrations of (2 5) X 1017 at room temperature. cm A prismlike crystal of CdSnP2 ~sshown in fig. 1. The largest facet is a {l 12} plane and the prism axis is the (111) axis as reported by Shay et al. [4]. The index of the facet was confirmed by reflection electron diffraction patterns. In fig. 1, two well-developed {101} facets also can be seen. Two types of the shapes of the cross section normal to the (111) axis -
_
___
Fig. l.A typical prismlike crystal of CdSnP2. 143
T. Matsumoto, 7’. Ishida / Etching study on CdSnP
144
2
plane and not on the ~112} mat plane as described
TYPE A
®
Z~
(11 2) (111)
_~,,,
~
N
- -
(11 ~) TYPE B
N
shiny plane corresponds the Cd—Sn plane or to the {112} P plane. Hereafter in thistoletter, we tentatively
(112)
7’@ ciru
/
(
later. The crystals of CdSnP2, which crystallize in the chalcopyrite structure, have two types of the {l 12} planes; one is the Cd Sn plane and the other is the P plane. It has not yet been determined whether the
,~
~7
N~
>
//
(11 2)
~TWINBOUNDARY Fig. 2. Two types of the cross sections perpendicular to the (111) prism axis. Triangular etch pits and a twin boundary line are shown schematically.
were found among the prismlike crystals. The two types, designated as type A and type B, are shown in fig. 2. Both of them have two fully-developed {l 12} facets unlike the reported habit of ZnSiP2 [5] or CdGeAs2 [6]. In the type A crystals, one {1 1 2} facet was shiny and the other {112} facet was mat. On the other hand, both of the two {1 12} facets of the type B crystals exhibited shiny surfaces. We observed deep etch pits only on the {1 12} shiny
__
designate the shiny plane as the (112) plane and the mat plane as the (Ti~)plane. The {101} facets looked shiny as the (112) facets to the naked eye. Prismlike crystals of CdSnP2 were immersed in the solution of 1 HF + 2 HNO3 + 2 H20 at room ternperature for about 150 mm, and etch figures revealed on each facet were observed with an optical microscope. Triangular etch pits were observed on the (112) shiny facets as shown in fig. 3. The triangular pits were elongated along the [ill] axis. An etched surface of the (1 1~)mat facet is shown in fig. 4. Triangular pyramidal figures were seen in contrast to the deep pits observed on the (112) shiny facets. Fig. 5 shows etch figures observed on the (101) facet.The etch figures are completely different from both those observed on the (112) shiny facet and those on the (112) mat facet. Two lines parallel to the [111] axis can be seen in fig. 5. We think them to be twin boundary lines. This twinning is the same as that observed in solution grown CdGeAs2 [6]. A prismlike
~ Fig. 3. Etch pits on the (112) shiny facet.
20 j~rn~
T. Matsumoto, 7’. Ishida
/ Etching study on
CdSnP
2
145
1(1, 1, 2)
+ II-
-~—
t
5pmI
Fig. 4. Triangular pyramidal etch figures revealed on the (112) mat facet.
crystal was cut and a surface perpendicular to the [ill] axis, which was the (114) plane in the case of c = 2a, was polished. The polished surface was etched with the above-mentioned solution at room temperature for about 180 mm. Triangular etch pits and twin boundary lines parallel to the [110] axis were
revealed as shown in fig. 6. It can be seen that the triangles of etch pits on one side of a twin boundary line are 180° rotated with respect to those on the opposite side of the twin boundary line (see also fig. 2). On the basis of the above observations, we concluded that the prismlike crystals of type B had the
4 Fig. 5. An etched surface of the (101) facet.
146
/ Etching study on
T. Matsumoto, T. Ishida
ff14)
~
~1 -
2
,~‘
.~
‘~4:
CdSnP
______
~
_
no
Fig. 6. Etch pits and twin boundary lines observed on the plane perpendicular to the (111> axis.
odd number of twin planes parallel to the {112} plane, and that those of type A had the even number (including zero) of the twin planes. The twinning was observed in many of prismlike crystals.
[2] E. Buehler, J.H. Wernick and J.L. Shay, Mater. Res. Bull. 6 (1971) 303.
The authors would like to thank T. Kanemaru for crystal growth, and H. Osada for electron’diffraction patterns. This work was partly supported by ScientifIc Research Grant-In-Aid, Special Project Research “Optical Guided-Wave Electronics”, from the Ministry of Education, Science and Culture, Japan.
[5]
References [1] J.L. Shay and J.H. Wernick, Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties, and Applications (Pergamon, Oxford, 1975).
[3] E.Buehler and J.H. Wernick, J. Crystal Growth 8 (1971) [4] J.L. Shay, E. Buehler and J.H. Wernick, Phys. Rev. B2 ~v,
E. Buehler and J.H. Wernick, Phys. Rev.
B2 (1910) 960. [6] R.S. Feigelson, R.K. Route and H.W. Swarts, 3. Crystal Growth 28 (1975) 138.
LETTER TO THE EDITORS ETCHING STUDY ON CdSnP2 PRISMLIKE CRYSTALS Takashi MATSUIMOTO and Tetsuro ISHIDA Department of Electronic Engineering, Yamanashi University, Takeda-4, Kofu 400, Japan Received 8 August 1980
Prismlike crystals of CdSnP2 grown from a tin solution were etched in a solution of 1 HF + 2 HNO3 + 2 H20. Characteristic etch figures were revealed on the (112), (112) and (101) facets. On the planes perpendicular to the (111) axis, etch pits and twin boundary lines were observed. Twin planes parallel to the {l 12} plane were found in many of the prismlike crystals.
Cadmium tin diphosphide (CdSnP2) is one of the chalcopyrite semiconductors, and considerable work has been done on its electronic structure and luminescent properties [1]. In order to use this material for electronic devices, device technology such as chemical etching is required. However, little has been reported on either etchants or etching properties of CdSnP2 crystals. In this letter, we describe the characteristics of etch figures observed on the facets of solution grown prismlike CdSnP2 crystals. Crystals of CdSnP 2 were grown from a tin solution by slow cooling [2,3]. A mixture of atomic composition of 33% Cd, 6.7% P and 90% Sn was sealed in an evacuated quartz ampoule at a pressure lower than iO~ Torr. The ampoule was heated to 800°C and held at this temperature for 28 h to homogenize the melt. The melt was slowly cooled at a rate of 5 K/h
I
_
from 600°C to 290°C according to the CdP2—Sn phase diagram [2]. The tin and the grown crystals were separated in hot glycerin at a temperature higher than the melting point of tin (232°C).Strain-free prismlike crystals were obtained by means of this technique. Residual tin attached to the grown crystals was removed by dissolution in a solution of 1 HF + 2 HNO3 + 2 1120. Crystals not intentionally doped were of n-type with resistivities of 0.01 0.03 &2 cm 3and electron concentrations of (2 5) X 1017 at room temperature. cm A prismlike crystal of CdSnP2 ~sshown in fig. 1. The largest facet is a {l 12} plane and the prism axis is the (111) axis as reported by Shay et al. [4]. The index of the facet was confirmed by reflection electron diffraction patterns. In fig. 1, two well-developed {101} facets also can be seen. Two types of the shapes of the cross section normal to the (111) axis -
_
___
Fig. l.A typical prismlike crystal of CdSnP2. 143
T. Matsumoto, 7’. Ishida / Etching study on CdSnP
144
2
plane and not on the ~112} mat plane as described
TYPE A
®
Z~
(11 2) (111)
_~,,,
~
N
- -
(11 ~) TYPE B
N
shiny plane corresponds the Cd—Sn plane or to the {112} P plane. Hereafter in thistoletter, we tentatively
(112)
7’@ ciru
/
(
later. The crystals of CdSnP2, which crystallize in the chalcopyrite structure, have two types of the {l 12} planes; one is the Cd Sn plane and the other is the P plane. It has not yet been determined whether the
,~
~7
N~
>
//
(11 2)
~TWINBOUNDARY Fig. 2. Two types of the cross sections perpendicular to the (111) prism axis. Triangular etch pits and a twin boundary line are shown schematically.
were found among the prismlike crystals. The two types, designated as type A and type B, are shown in fig. 2. Both of them have two fully-developed {l 12} facets unlike the reported habit of ZnSiP2 [5] or CdGeAs2 [6]. In the type A crystals, one {1 1 2} facet was shiny and the other {112} facet was mat. On the other hand, both of the two {1 12} facets of the type B crystals exhibited shiny surfaces. We observed deep etch pits only on the {1 12} shiny
__
designate the shiny plane as the (112) plane and the mat plane as the (Ti~)plane. The {101} facets looked shiny as the (112) facets to the naked eye. Prismlike crystals of CdSnP2 were immersed in the solution of 1 HF + 2 HNO3 + 2 H20 at room ternperature for about 150 mm, and etch figures revealed on each facet were observed with an optical microscope. Triangular etch pits were observed on the (112) shiny facets as shown in fig. 3. The triangular pits were elongated along the [ill] axis. An etched surface of the (1 1~)mat facet is shown in fig. 4. Triangular pyramidal figures were seen in contrast to the deep pits observed on the (112) shiny facets. Fig. 5 shows etch figures observed on the (101) facet.The etch figures are completely different from both those observed on the (112) shiny facet and those on the (112) mat facet. Two lines parallel to the [111] axis can be seen in fig. 5. We think them to be twin boundary lines. This twinning is the same as that observed in solution grown CdGeAs2 [6]. A prismlike
~ Fig. 3. Etch pits on the (112) shiny facet.
20 j~rn~
T. Matsumoto, 7’. Ishida
/ Etching study on
CdSnP
2
145
1(1, 1, 2)
+ II-
-~—
t
5pmI
Fig. 4. Triangular pyramidal etch figures revealed on the (112) mat facet.
crystal was cut and a surface perpendicular to the [ill] axis, which was the (114) plane in the case of c = 2a, was polished. The polished surface was etched with the above-mentioned solution at room temperature for about 180 mm. Triangular etch pits and twin boundary lines parallel to the [110] axis were
revealed as shown in fig. 6. It can be seen that the triangles of etch pits on one side of a twin boundary line are 180° rotated with respect to those on the opposite side of the twin boundary line (see also fig. 2). On the basis of the above observations, we concluded that the prismlike crystals of type B had the
4 Fig. 5. An etched surface of the (101) facet.
146
/ Etching study on
T. Matsumoto, T. Ishida
ff14)
~
~1 -
2
,~‘
.~
‘~4:
CdSnP
______
~
_
no
Fig. 6. Etch pits and twin boundary lines observed on the plane perpendicular to the (111> axis.
odd number of twin planes parallel to the {112} plane, and that those of type A had the even number (including zero) of the twin planes. The twinning was observed in many of prismlike crystals.
[2] E. Buehler, J.H. Wernick and J.L. Shay, Mater. Res. Bull. 6 (1971) 303.
The authors would like to thank T. Kanemaru for crystal growth, and H. Osada for electron’diffraction patterns. This work was partly supported by ScientifIc Research Grant-In-Aid, Special Project Research “Optical Guided-Wave Electronics”, from the Ministry of Education, Science and Culture, Japan.
[5]
References [1] J.L. Shay and J.H. Wernick, Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties, and Applications (Pergamon, Oxford, 1975).
[3] E.Buehler and J.H. Wernick, J. Crystal Growth 8 (1971) [4] J.L. Shay, E. Buehler and J.H. Wernick, Phys. Rev. B2 ~v,
E. Buehler and J.H. Wernick, Phys. Rev.
B2 (1910) 960. [6] R.S. Feigelson, R.K. Route and H.W. Swarts, 3. Crystal Growth 28 (1975) 138.