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Structural properties of InN films grown on GaAs substrates: observation of the zincblende polytpe
Journal of Crystal Growth 127 (1993) 204—208 North-Holland
j~
~
CRYSTAL
GROWTH
Structural properties of InN films grown on GaAs substrates: observation of the zincblende polytype S. Strite a,b,c D. Chandrasekhar and H. Morkoç a,b
d
David J. Smith
d,e
j• Sane!
f,1
H. Chen
b,f
N. Teraguchi
‘~‘
Coordinated Science Laboratory, University of Illinois, Urbana, Illinois 61801, USA ~Materials Research Laboratory, University of illinois, Urbana, Illinois 61801, USA ‘Department of Physics, University of Illinois, Urbana, Illinois 61801, USA d Center for Solid State Science, Arizona State University, Tempe, Arizona 85287, USA ‘Department of Physics, Arizona State Unit ersity, Tempe, Arizona 85287, USA ~Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA
We report the first observation of the zincblende polytype of the InN semiconductor, InN films were grown on vicinal (100) GaAs substrates by plasma enhanced molecular beam epitaxy. Transmission electron microscopy showed the InN films to be highly defective with both zincblende and wurtzite domains being present. The zincblende domains were epitaxially oriented to the substrate. The wurtzite InN had its c axis normal to the Kill) zincblende planes which suggests stacking faults as the nucleation mechanism of the hexagonal phase. X-ray diffractometry measured a lattice constant a 0.498 ±0.001 nm for the zincblende InN polytype and a = 0.36+0.01 nm and c = 0.574±0.001nm for the wurtzite polytype.
1. Introduction The Ill—V nitride semiconductors GaN, A1N and InN are of interest for their potential as optical materials which are active from the orange into the ultraviolet [1,21. These materials have an equilibrium crystal structure which is wurtzite. The bandgaps of the wurtzite nitride semiconductors are all direct and their alloys have a continuous range of direct bandgap values from 1.9 eV for InN to 3.4 eV for GaN to 6.2 eV for AIN. It has been known for some years that GaN, under proper growth conditions, can be made to crystallize in a zincblende phase [3,4]. Moreover, the zincblende BN polytype, also a Ill—V nitride semiconductor, can be readily grown [1]. Recently, two groups [5,61have reported the existence of zincblende AIN. The zincblende nitrides represent a new material system which has potential for short waveOn leave from the Nuclear Research Center, Negev, Box 9001, Beer-Sheva, 84190, Israel. 0022-0248/93/$06.00 © 1993
—
p.o.
length optical device applications. Recent research activity on the zincblende Ill—V nitrides has begun to determine their physical properties. Zincblende GaN has been shown to be a direct gap semiconductor whose bandgap is slightly less than its wurtzite counterpart [7]. Lambrecht and Segall have calculated the band structure of zincblende AIN and predicted it to have a 5.11 eV indirect bandgap [81, significantly different from the 6.2 eV direct bandgap of the wurtzite polytype. In the only published work pertaining to zincblende InN of which we are aware, Jenkins et al. [9] predicted that zincblende InN would have a direct bandgap which is roughly the same as the wurtzite polytype. Little effort has been directed towards determining whether a zincblende polytype of the remaining Ill—V nitride semiconductor, InN, exists. In this paper, we describe the structural properties of InN films grown on GaAs (100) vicinal substrates, and confirm, for the first time, the existence of a zincblende InN polytype. We also observe directly that stacking faults present in the (111)
Elsevier Science Publishers B.V. All rights reserved
S. Strife et al.
/ Structural properties of InN films grown on
GaAs substrates
205
4° towards [0111 was outgassed and the buffer oxide desorbed in the usual manner. An unintentionally doped GaAs buffer layer was then grown to obtain the cleanest, most defect-free surface possible for heteroepitaxy. InN growth was initiated by closing the Ga shutter while the sample was cooled to 520°C.The As flux was removed at 540°C.After a total delay of appoximately 5 mm, the nitrogen plasma was lit and the In shutter was opened. InN was grown at a rate of 100 nm/h at approximately 520°C at a nitrogen pressure of 3 x i0~ Torr. Typical InN film thicknesses were of the order of 500 nm. Hall measurements were performed by soldering In contacts to an unpatterned film. Like most InN samples reported to date, our films were highly conductive, having an electron concentration of n = 1020 cm3 with a mobility ~ = 220 cm2/V s. .
_______
•‘1~~ ~ I Fig. 1. Transmission electron micrograph of the InN/GaAs interface. An unintentionally deposited InAs interlayer (~80 nm) is present between the GaAs substrate and the InN films, A high density of planar defects growing on both KIll) planes are visible in the InN epilayer.
planes of the zincblende InN serve to nucleate domains of wurtzite InN material,
2. Experiment The samples reported here were all grown in a Perkin-Elmer 430 molecular beam epitaxy (MBE) system. Nitrogen was taken from liquid nitrogen boil-off, filtered first for particulates and finally for impurities using a Semigas NanochemTM filter. The high purity nitrogen was ignited into a plasma by either a Wavemat MPDRTM or an ASTEX CECRTM electron cyclotron resonance plasma source in order to produce a flux of highly reactive atomic and ionized species. Initially, a semi-insulating (100) GaAs substrate misoriented
3. Results and discussion
Transmission electron microscopy (TEM) was used to characterize the microstructure of the heterointerface and the bulk InN film. A low resolution image recorded in the cross-sectional geometry (fig. 1) reveals the existence of an unintentionally grown InAs interlayer between the GaAs and InN which is roughly 80 nm thick. The As background pressure in the chamber was insufficient to account for the growth of such a thick InAs layer. We surmise that As was drawn from the GaAs substrate to react with impinging In atoms on the surface. An inclusion of InAs into the GaAs substrate is clearly visible in fig. 1, which lends weight to the supposition of some sort of reaction with the substrate. The InAs interlayer could likely be eliminated through the use of a GaN buffer layer. The InN film is highly disordered with a large number of stacking faults running along the (111) planes. These planar defects are similar to those seen in zincblende GaN grown on cubic SiC [10] or (100) GaAs [11]. High resolution (HR) TEM images such as those shown in fig. 2 reveal the coexistence of both InN polytypes. In some regions, perfect zincblende InN is obtained, whereas other areas show the wurtzite phase (fig. 2a). The zincblende InN is
206
5. Strite ci a!.
/ Structural properties of InN films grown on
oriented epitaxially to the GaAs substrate while the c axis of the wurtzite InN is normal to the zincblende (111) plane. In the most heavily faulted regions (fig. 2b), it becomes impossible to identify either phase because there is no long range stacking order, Stacking faults are a critical defect for materials which can crystallize in both the wurtzite and zincblende structures. The major difference between these two polytypes is the stacking sequence of the planes along the [1111 direction. The zincblende structure is ordered in an ABCABC sequence, whereas wurtzite has an ABABAB stacking. Therefore, a stacking fault in zincblende material could generate the wurtzite phase and vice versa. This behavior was first observed in the Ill—V nitrides by Lei and Moustakas [12]. They reported X-ray diffraction data proving the existence of zincblende GaN domains nucleated at stacking faults in a bulk wurtzite GaN film. Our results represent the first case of a wurtzite nitride polytype being nucleated from the zincblende phase. In our films, the stacking faults serve to relieve the strain arising from the
_
Fig.
~.
____
GaAs substrates
large lattice mismatch between the InN and the substrate, as well as to allow the nucleation of the more stable wurtzite InN in favor of the metastable zincblende material. This picture is probably also valid in the case of zincblende A1N which was reported to also fault heavily [5]. At present, there is insufficient experimental cvidence to confidently identify a strong preference in the GaN system between the wurtzite and zincblende orientations. On the one hand, all GaN grown on zincblende (111) substrates, which provide no template for a preferential stacking sequence, as well as all polycrystalline material, has been observed to be wurtzite [21. However, zincblende GaN has been grown on basal plane sapphire [131, a hexagonal substrate, and Lei and Moustakas [12] have observed the nucleation of bulk zincblende GaN in their wurtzite films. Clearly, the tendency of the Ill—V nitrides to suffer from high densities of stacking faults is a major hindrance to the growth of high quality material of either polytype and a better understanding of the nature of this phenomenon is of importance.
-~------J
I ligh resolution electron micrograph~of he InN film: (a) region showing a boundary between v. urtzitc ( upper left) and zincblende (lower right) domains; (h) region of heavily faulted material which has no long range stacking order.
S. Strite et a!.
/ Structural properties of InN films grown on
X-ray diffractometry was used to determine the lattice constants of the InN phases. Both the (200) (20 = 36.037°)and the (400) (20 = 76.520°) zincblende InN peaks were observed in the 0—20 scan shown in fig. 3, which confirms the zincblende material to be epitaxial to the substrate. To determine the lattice constant and the experimental error, the GaAs (200) K~and the GaAs (400) Ka1 and Ka2 peaks were used as a standard to correct for instrumental shift and broadening. From the (200) and (400) InN peaks, the zincblende InN lattice constant was determined to be a = 0.498 ±0.001 nm. Measurements of HRTEM micrographs and selected area diffraction patterns, while intrinsically less accurate, gave a value of 0.495 ±0.005 nm. A rocking curve taken of the (200) InN peak had a full width at half maximum of 3° after instrumental width correction, which is quite large and is in accordance with the poor overall film quality observed by HRTEM. The wurtzite phase was measured by rotating the sample to 29 = 51.596°and x 65° aligned to the (110) peak of the wurtzite domains observed by TEM. This orientation is revealing because it is nonnal to the stacking direction, i.e. [0011for wurtzite, [111] for zincblende. When rotating around the (110) axis (4 axis in our geometry) the
GaAs substrates
207
2500 2250 2000
~1250
750 500 250
120-9060-300
306090120
170180
.
Fig. 4. X-ray 4-scan around the (110) wurtzite axis reveals the four Kilo) peaks at roughly 90°intervals confirming that the stacking of the (001) wurtzite planes is normal to the observed stacking fault planes.
ABABAB stacking of the wurtzite polytype is expected to produce the four equally spaced peaks corresponding to the four K110~planes. This was indeed experimentally observed (fig. 4), which confirms the relationship of the wurtzite InN with the stacking faults as seen by TEM. The lattice constants of the wurtzite polytype were calculated to be a = 0.36 ±0.01 nm from the (110) peak and c = 0.574 ±0.001 nm from the (002) peak, which are in good agreement with previous work [21.
4. Conclusion
5000C1 45000 40000 35000
C~As(2OO)
30000 ~25000~
~5(2oQ)
20000 15000: 10000
5-74(400)
5000 0
I~
A
],!l,,!,I!!,!c
25
30
35
40
~,-,—~—,—~—U,—,—~fl-m-’ -,
45
Thetc(~)
60
,
65
1 ~
70
75
80
Fig. 3. X-ray data from an InN/GaAs layer showing the (200) and (400) peaks of the epitaxial zincblende InN material and the GaAs substrate,
In summary, we have grown InN films on GaAs substrates by MBE and, for the first time, the zincblende polytype of InN has been identified. A room temperature equilibrium lattice constant of a = 0.498 ±0.001 nm was measured by X-ray diffraction for zincblende InN. A microstructural study of the InN films by transmission electron microscopy revealed a high density of stacking fault defects from which wurtzite domains of InN were nucleated. At present, the high density of stacking faults present in nitride films of both polytypes appears to represent a major hindrance in efforts to grow high quality, single phase Ill—V nitride crystals.
208
5. Strite ci a!.
/ Structural properties of InN films grown on
Acknowledgements This work was supported by the Office for Naval Research contract #N00014-89-J-1780. Electron microscopy was conducted at the Center for High Resolution Microscopy at Arizona State University, supported by NSF Grant DMR 8913384. The X-ray diffraction portion of this work benefitted from the use of the University of Illi nois Materials Research Laboratory’s facility which is supported by the US Department of Energy under contract DE-ACO2-76ER01198. We wish to thank M. Yoder for his enthusiasm for and encouragement of this effort and Dr. M.S. UnlU, Dr. M.E. Lin, A. Salvador, Dr. B. Sverdlov, and A.L. Demirel for their assistance at various stages of this work. S. S. wishes to acknowledge the support of an AFOSR Graduate Fellowship. References [1] R.F. Davis, Proc. IEEE 79 (1991) 702. [2] S. Strite and H. Morkoç, J. Vacuum Sci. Technol. B 10 (1992) 1237.
[31W.
GaAs substrates
Seifert and A. Tempel, Phys. Status Solidi (a) 23 (1974) K39. 141 M. Mizuta, S. Fujieda, Y. Matsumoto and T. Kawamura, Japan. J. Appi. Phys. 25 (1986) L945; S. Fujieda and Y. Maisumoto, Japan. J. Appl. Phys. 30 (1991) L1665. 151 R.F. Davis, M.J. Paisley and Z. Sitar, Annual Progress Report, Contract #N00014-86-K-0686, June 1, 1989. 161 1. Petrov, F. Mojab, R.C. Powell, J.E. Greene, L. Hultman and J.-E. Sundgren, AppI. Phys. Letters 60 (1992) 2491. 171 R.C. Powell, G.A. Tomasch, Y.W. Kim, J.A. Thornton and J.E. Greene, Mater. Res. Soc. Symp. Proc. 162 (1990) 525. [81W.R.L. Lambrecht and B. Segall, Phys. Rev. B 43 (1991) 7070 [91crostruc. D. Jenkins, R. Hong and J. Dow, Superlattices Mi3 (1987) 365. 110] M.J. Paisley, Z. Sitar, J.B. Posthill and R.F. Davis, J. Vacuum Sci. Technol. A 7 (1989) 701. [11] S. Strite, J. Ruan, Z. Li, N. Manning, A. Salvador, I-I. Chen, D. Smith, W. Choyke and H. Morkoç, J. Vacuum Sci. Technol B 9 (1991) 1924. [12] T. Lei and T.D. Moustakas, Mater. Res. Soc. Symp. Proc. 242 (1992) 433. [13] T.P. Humphreys, C.A. Sukow, R.J. Nemanich, J.B. Posthill, R.A. Rudder, S.V. Hattangady and R.J. Markunas, Mater. Res. Soc. Symp. Proc. 162 (1990) 531.
j~
~
CRYSTAL
GROWTH
Structural properties of InN films grown on GaAs substrates: observation of the zincblende polytype S. Strite a,b,c D. Chandrasekhar and H. Morkoç a,b
d
David J. Smith
d,e
j• Sane!
f,1
H. Chen
b,f
N. Teraguchi
‘~‘
Coordinated Science Laboratory, University of Illinois, Urbana, Illinois 61801, USA ~Materials Research Laboratory, University of illinois, Urbana, Illinois 61801, USA ‘Department of Physics, University of Illinois, Urbana, Illinois 61801, USA d Center for Solid State Science, Arizona State University, Tempe, Arizona 85287, USA ‘Department of Physics, Arizona State Unit ersity, Tempe, Arizona 85287, USA ~Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, USA
We report the first observation of the zincblende polytype of the InN semiconductor, InN films were grown on vicinal (100) GaAs substrates by plasma enhanced molecular beam epitaxy. Transmission electron microscopy showed the InN films to be highly defective with both zincblende and wurtzite domains being present. The zincblende domains were epitaxially oriented to the substrate. The wurtzite InN had its c axis normal to the Kill) zincblende planes which suggests stacking faults as the nucleation mechanism of the hexagonal phase. X-ray diffractometry measured a lattice constant a 0.498 ±0.001 nm for the zincblende InN polytype and a = 0.36+0.01 nm and c = 0.574±0.001nm for the wurtzite polytype.
1. Introduction The Ill—V nitride semiconductors GaN, A1N and InN are of interest for their potential as optical materials which are active from the orange into the ultraviolet [1,21. These materials have an equilibrium crystal structure which is wurtzite. The bandgaps of the wurtzite nitride semiconductors are all direct and their alloys have a continuous range of direct bandgap values from 1.9 eV for InN to 3.4 eV for GaN to 6.2 eV for AIN. It has been known for some years that GaN, under proper growth conditions, can be made to crystallize in a zincblende phase [3,4]. Moreover, the zincblende BN polytype, also a Ill—V nitride semiconductor, can be readily grown [1]. Recently, two groups [5,61have reported the existence of zincblende AIN. The zincblende nitrides represent a new material system which has potential for short waveOn leave from the Nuclear Research Center, Negev, Box 9001, Beer-Sheva, 84190, Israel. 0022-0248/93/$06.00 © 1993
—
p.o.
length optical device applications. Recent research activity on the zincblende Ill—V nitrides has begun to determine their physical properties. Zincblende GaN has been shown to be a direct gap semiconductor whose bandgap is slightly less than its wurtzite counterpart [7]. Lambrecht and Segall have calculated the band structure of zincblende AIN and predicted it to have a 5.11 eV indirect bandgap [81, significantly different from the 6.2 eV direct bandgap of the wurtzite polytype. In the only published work pertaining to zincblende InN of which we are aware, Jenkins et al. [9] predicted that zincblende InN would have a direct bandgap which is roughly the same as the wurtzite polytype. Little effort has been directed towards determining whether a zincblende polytype of the remaining Ill—V nitride semiconductor, InN, exists. In this paper, we describe the structural properties of InN films grown on GaAs (100) vicinal substrates, and confirm, for the first time, the existence of a zincblende InN polytype. We also observe directly that stacking faults present in the (111)
Elsevier Science Publishers B.V. All rights reserved
S. Strife et al.
/ Structural properties of InN films grown on
GaAs substrates
205
4° towards [0111 was outgassed and the buffer oxide desorbed in the usual manner. An unintentionally doped GaAs buffer layer was then grown to obtain the cleanest, most defect-free surface possible for heteroepitaxy. InN growth was initiated by closing the Ga shutter while the sample was cooled to 520°C.The As flux was removed at 540°C.After a total delay of appoximately 5 mm, the nitrogen plasma was lit and the In shutter was opened. InN was grown at a rate of 100 nm/h at approximately 520°C at a nitrogen pressure of 3 x i0~ Torr. Typical InN film thicknesses were of the order of 500 nm. Hall measurements were performed by soldering In contacts to an unpatterned film. Like most InN samples reported to date, our films were highly conductive, having an electron concentration of n = 1020 cm3 with a mobility ~ = 220 cm2/V s. .
_______
•‘1~~ ~ I Fig. 1. Transmission electron micrograph of the InN/GaAs interface. An unintentionally deposited InAs interlayer (~80 nm) is present between the GaAs substrate and the InN films, A high density of planar defects growing on both KIll) planes are visible in the InN epilayer.
planes of the zincblende InN serve to nucleate domains of wurtzite InN material,
2. Experiment The samples reported here were all grown in a Perkin-Elmer 430 molecular beam epitaxy (MBE) system. Nitrogen was taken from liquid nitrogen boil-off, filtered first for particulates and finally for impurities using a Semigas NanochemTM filter. The high purity nitrogen was ignited into a plasma by either a Wavemat MPDRTM or an ASTEX CECRTM electron cyclotron resonance plasma source in order to produce a flux of highly reactive atomic and ionized species. Initially, a semi-insulating (100) GaAs substrate misoriented
3. Results and discussion
Transmission electron microscopy (TEM) was used to characterize the microstructure of the heterointerface and the bulk InN film. A low resolution image recorded in the cross-sectional geometry (fig. 1) reveals the existence of an unintentionally grown InAs interlayer between the GaAs and InN which is roughly 80 nm thick. The As background pressure in the chamber was insufficient to account for the growth of such a thick InAs layer. We surmise that As was drawn from the GaAs substrate to react with impinging In atoms on the surface. An inclusion of InAs into the GaAs substrate is clearly visible in fig. 1, which lends weight to the supposition of some sort of reaction with the substrate. The InAs interlayer could likely be eliminated through the use of a GaN buffer layer. The InN film is highly disordered with a large number of stacking faults running along the (111) planes. These planar defects are similar to those seen in zincblende GaN grown on cubic SiC [10] or (100) GaAs [11]. High resolution (HR) TEM images such as those shown in fig. 2 reveal the coexistence of both InN polytypes. In some regions, perfect zincblende InN is obtained, whereas other areas show the wurtzite phase (fig. 2a). The zincblende InN is
206
5. Strite ci a!.
/ Structural properties of InN films grown on
oriented epitaxially to the GaAs substrate while the c axis of the wurtzite InN is normal to the zincblende (111) plane. In the most heavily faulted regions (fig. 2b), it becomes impossible to identify either phase because there is no long range stacking order, Stacking faults are a critical defect for materials which can crystallize in both the wurtzite and zincblende structures. The major difference between these two polytypes is the stacking sequence of the planes along the [1111 direction. The zincblende structure is ordered in an ABCABC sequence, whereas wurtzite has an ABABAB stacking. Therefore, a stacking fault in zincblende material could generate the wurtzite phase and vice versa. This behavior was first observed in the Ill—V nitrides by Lei and Moustakas [12]. They reported X-ray diffraction data proving the existence of zincblende GaN domains nucleated at stacking faults in a bulk wurtzite GaN film. Our results represent the first case of a wurtzite nitride polytype being nucleated from the zincblende phase. In our films, the stacking faults serve to relieve the strain arising from the
_
Fig.
~.
____
GaAs substrates
large lattice mismatch between the InN and the substrate, as well as to allow the nucleation of the more stable wurtzite InN in favor of the metastable zincblende material. This picture is probably also valid in the case of zincblende A1N which was reported to also fault heavily [5]. At present, there is insufficient experimental cvidence to confidently identify a strong preference in the GaN system between the wurtzite and zincblende orientations. On the one hand, all GaN grown on zincblende (111) substrates, which provide no template for a preferential stacking sequence, as well as all polycrystalline material, has been observed to be wurtzite [21. However, zincblende GaN has been grown on basal plane sapphire [131, a hexagonal substrate, and Lei and Moustakas [12] have observed the nucleation of bulk zincblende GaN in their wurtzite films. Clearly, the tendency of the Ill—V nitrides to suffer from high densities of stacking faults is a major hindrance to the growth of high quality material of either polytype and a better understanding of the nature of this phenomenon is of importance.
-~------J
I ligh resolution electron micrograph~of he InN film: (a) region showing a boundary between v. urtzitc ( upper left) and zincblende (lower right) domains; (h) region of heavily faulted material which has no long range stacking order.
S. Strite et a!.
/ Structural properties of InN films grown on
X-ray diffractometry was used to determine the lattice constants of the InN phases. Both the (200) (20 = 36.037°)and the (400) (20 = 76.520°) zincblende InN peaks were observed in the 0—20 scan shown in fig. 3, which confirms the zincblende material to be epitaxial to the substrate. To determine the lattice constant and the experimental error, the GaAs (200) K~and the GaAs (400) Ka1 and Ka2 peaks were used as a standard to correct for instrumental shift and broadening. From the (200) and (400) InN peaks, the zincblende InN lattice constant was determined to be a = 0.498 ±0.001 nm. Measurements of HRTEM micrographs and selected area diffraction patterns, while intrinsically less accurate, gave a value of 0.495 ±0.005 nm. A rocking curve taken of the (200) InN peak had a full width at half maximum of 3° after instrumental width correction, which is quite large and is in accordance with the poor overall film quality observed by HRTEM. The wurtzite phase was measured by rotating the sample to 29 = 51.596°and x 65° aligned to the (110) peak of the wurtzite domains observed by TEM. This orientation is revealing because it is nonnal to the stacking direction, i.e. [0011for wurtzite, [111] for zincblende. When rotating around the (110) axis (4 axis in our geometry) the
GaAs substrates
207
2500 2250 2000
~1250
750 500 250
120-9060-300
306090120
170180
.
Fig. 4. X-ray 4-scan around the (110) wurtzite axis reveals the four Kilo) peaks at roughly 90°intervals confirming that the stacking of the (001) wurtzite planes is normal to the observed stacking fault planes.
ABABAB stacking of the wurtzite polytype is expected to produce the four equally spaced peaks corresponding to the four K110~planes. This was indeed experimentally observed (fig. 4), which confirms the relationship of the wurtzite InN with the stacking faults as seen by TEM. The lattice constants of the wurtzite polytype were calculated to be a = 0.36 ±0.01 nm from the (110) peak and c = 0.574 ±0.001 nm from the (002) peak, which are in good agreement with previous work [21.
4. Conclusion
5000C1 45000 40000 35000
C~As(2OO)
30000 ~25000~
~5(2oQ)
20000 15000: 10000
5-74(400)
5000 0
I~
A
],!l,,!,I!!,!c
25
30
35
40
~,-,—~—,—~—U,—,—~fl-m-’ -,
45
Thetc(~)
60
,
65
1 ~
70
75
80
Fig. 3. X-ray data from an InN/GaAs layer showing the (200) and (400) peaks of the epitaxial zincblende InN material and the GaAs substrate,
In summary, we have grown InN films on GaAs substrates by MBE and, for the first time, the zincblende polytype of InN has been identified. A room temperature equilibrium lattice constant of a = 0.498 ±0.001 nm was measured by X-ray diffraction for zincblende InN. A microstructural study of the InN films by transmission electron microscopy revealed a high density of stacking fault defects from which wurtzite domains of InN were nucleated. At present, the high density of stacking faults present in nitride films of both polytypes appears to represent a major hindrance in efforts to grow high quality, single phase Ill—V nitride crystals.
208
5. Strite ci a!.
/ Structural properties of InN films grown on
Acknowledgements This work was supported by the Office for Naval Research contract #N00014-89-J-1780. Electron microscopy was conducted at the Center for High Resolution Microscopy at Arizona State University, supported by NSF Grant DMR 8913384. The X-ray diffraction portion of this work benefitted from the use of the University of Illi nois Materials Research Laboratory’s facility which is supported by the US Department of Energy under contract DE-ACO2-76ER01198. We wish to thank M. Yoder for his enthusiasm for and encouragement of this effort and Dr. M.S. UnlU, Dr. M.E. Lin, A. Salvador, Dr. B. Sverdlov, and A.L. Demirel for their assistance at various stages of this work. S. S. wishes to acknowledge the support of an AFOSR Graduate Fellowship. References [1] R.F. Davis, Proc. IEEE 79 (1991) 702. [2] S. Strite and H. Morkoç, J. Vacuum Sci. Technol. B 10 (1992) 1237.
[31W.
GaAs substrates
Seifert and A. Tempel, Phys. Status Solidi (a) 23 (1974) K39. 141 M. Mizuta, S. Fujieda, Y. Matsumoto and T. Kawamura, Japan. J. Appi. Phys. 25 (1986) L945; S. Fujieda and Y. Maisumoto, Japan. J. Appl. Phys. 30 (1991) L1665. 151 R.F. Davis, M.J. Paisley and Z. Sitar, Annual Progress Report, Contract #N00014-86-K-0686, June 1, 1989. 161 1. Petrov, F. Mojab, R.C. Powell, J.E. Greene, L. Hultman and J.-E. Sundgren, AppI. Phys. Letters 60 (1992) 2491. 171 R.C. Powell, G.A. Tomasch, Y.W. Kim, J.A. Thornton and J.E. Greene, Mater. Res. Soc. Symp. Proc. 162 (1990) 525. [81W.R.L. Lambrecht and B. Segall, Phys. Rev. B 43 (1991) 7070 [91crostruc. D. Jenkins, R. Hong and J. Dow, Superlattices Mi3 (1987) 365. 110] M.J. Paisley, Z. Sitar, J.B. Posthill and R.F. Davis, J. Vacuum Sci. Technol. A 7 (1989) 701. [11] S. Strite, J. Ruan, Z. Li, N. Manning, A. Salvador, I-I. Chen, D. Smith, W. Choyke and H. Morkoç, J. Vacuum Sci. Technol B 9 (1991) 1924. [12] T. Lei and T.D. Moustakas, Mater. Res. Soc. Symp. Proc. 242 (1992) 433. [13] T.P. Humphreys, C.A. Sukow, R.J. Nemanich, J.B. Posthill, R.A. Rudder, S.V. Hattangady and R.J. Markunas, Mater. Res. Soc. Symp. Proc. 162 (1990) 531.