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Si(001) grown by low temperature MOCVD process
Surface Science 267 (1992) 47-49 North-Holland
S u r f a c e science ~5..:..-..
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Crystallographic and optical properties of InP/Si(O01) grown by low temperature MOCVD process M. Grundmann, A. Krost, D. Bimberg Technische Universith't Berlin, Institut fiir Festk6rperphysik L Hardenbergstr. 36, W-IO00 Berlin 12, Germany
Received 31 May 1991; accepted for publication 27 June 1991
Growth of antiphase domain free lnP on St(001) is reported using a low temperature metalorganic chemical vapor deposition process without any preannealing of the substrate. The residual stress (typically 6-7 x 10-4), the tilt and the optical properties (best spectral broadening FWHM = 3.0 meV) of the lnP epilayers are characterized.
1. Introduction We have recently p r e s e n t e d a low t e m p e r a t u r e metal organic chemical vapor deposition ( M O C V D ) procedure for antiphase d o m a i n ( A P D ) free growth of InP on Si [1]. This process does not include any high t e m p e r a t u r e annealing, and is thus compatible with optoelectronic integration on St. It is ,~he purpose of this paper to characterize the crystallographic and optical properties of the epitaxial InP layers.
2. Experimental Details about the growth procedure may be found in [1]. We would like to summarize the growth procedure briefly: As substrates we use Si(001) misoriented along [110] with off-cut angles 0 varying from 0.8 ° to 6.0 °. We use a two ,3t~pa ~,IIUWUlprOUCklHIe" after repeated wet chemical oridation and oxide reme"al with 2.5% H F we grow at T>. = 400 ° C a 5.q nm thick InP buf~cr layer using a high V / I l l ratio of 3100 at a growth rate of 0.6 t z m / h . Typical growfl p a r a m e t e r s of the second layer are T = 640 ° C, V / I I I ,'atio of 250 and a growth rate of 2 - 3 t x m / h . We obtain mirror-like surfaces. N o high t e m p e r a t u r e an-
nealing step of the Si substrate prior to epitaxy is used.
3. Charader~zafion On Si with sufficient off-cut we obtain APDfree InP layers (e.g. for 0 = 4 ~' and Tt, - 4 0 0 ° (7) [1,2]. The inhomogeneous broadening of the (004) rocking curve, measured with double crystal X-ray diffraction ( D X D ) , is substantially reduced with increasing layer thickness d; we found F W H M ~ d - ° s [1], indicating that the d o m i n a n t process is a two-dislocation annihilation prccess. A typical value for X-ray diffraction b r o a d e n i n g is F W H M = 258 arcsec for d = 8/.tm. T h e etch pit density revealed by the Huber etch [3] is reduced from over l0 s c m - 2 for d = 1.3 ~tm to 3 x 107 cm -2 for d = 8 g m . With D X D we have m e a s u r e d the residual stress in the l n g and the relative tilt /3 of the ~nP epilaycr with respect to the Si substratc as a function of layer thickness d and off-orientation 0. The results are summarized in fig. 1. The initial stress of about k a / a o = 8% in the InP is compressive. After the growth of some 100 nm this stress is completely relieved plastically via formation of dislocations. During cooling from
11039-6028/92/$05.(1(1 .c 1092 - Elsevier Science Publishers B.V. and Yamad:! Science Foundation. All rights reserved
M. Gmndmann et al. , / L o w T MOCVD grown lnP / Si(O01)
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Fig. 1. Residual in-plane stress (a, c) and tilt (b, d) of the InP epilayer as a function of layer thickness for constant off-cut 0 = 3.8 ° (a, b) and as a function of off-cut for constant layer thickness d = 2.7/xm (c, d).
growth temperature to room temperature after epitaxy a tensile thermal stress eth is generated due to the different thermal expansion coefficients of InP and Si. For layer thickness d >_ 0.7 ~ m we find eth = 6-7 × 10 -4 (fig. la). This value is much smaller than for G~As layers of similar thickness on Si. Fig. lc shows that the residual stress is independent of the off-cut, as expected. The lnP layer is slightly tilted with respect to the Si substrate; the tilt has the same direction as the off-cut ([I-f0]). For constant off-cut the tilt is independent of the layer thickness for d >_ 0.7 g m (,fig. lb); this observation suggests that the tilt is connected with the plastic strain relaxation. Wit': increasing off-cut the tilt shows a linear increase (fig. ld). For the overgrowth of InP on Si one expects a tilt along the opposite direction of the off-cut ([110]) ~theo-- Aa/ao tan 0 (in the case of biatomic steps) [4]; for small angles 0/3th,:,,/00 = --290 arcsec/deg is predicted. Our experimental result of O/3~xp/00 = + 45 arcsec/deg implies that a mechanism exists which accommodates +335 arcsec/deg. Due to the linear dependence of /3 on 0 this mechanism is probably related to the absolute number of steps on the vicinat surface. Jt has bccn shown lot G a A s / S i that the dislocations can have their (110) Burgers vectors in the interface plane (type I, edge dislocation) or inclined to the interface (type II, 60 ° dislocation) [5]. Type I dislocations lead to no tilt of the
overlayer. The observed tilt can be explained by the preferred nucleation of type lI dislocations with Burgers vector b having a positive z-component (b+) compared to those with negative zcomponent (b_). The excess (b+)-(b_) determines the macroscopic tilt; in our case at about every 10th step on the vicinal substrate a b+ dislocation is generated without its b counterpart (independently from the off-cut!). With the reduction of rocking curve broadening also the optical properties are improved with increasing thickness. At low temperature the photoluminescence (PL) spectrum is dominated by shallow donor related luminescence. The peak broadening is reduced and the integrated intensity increases with increasing layer thickness (fig. 2). For large d the spectra of layers with and without APD's do not differ significantly. For small layer thickness the APD's induce larger inhomogeneities. But due to the fact that nonradiative recombination centers are concentrated at the domain boundaries [6], the total quantum efficiency is larger compared to layers without APD's. The smallest PL peak broadening obtained is FWHM = 3.0 meV for d - 8 ~ m and an
InP on $1 (001) • 0.8' off-cut ,~ 3 8 off-cut
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Fig. 2. Photolunfincsccncc peak broadening and integrated intensity :,t T = 2 K for layers with (0 = 0.8 °) and without (0 = 3.8 o ) APD's as a function of !nP I,~yer thickness d. The arrows denote the values for a 2 ~tm | n P layer on InP:Fe.
M. Gmndmann et aL / Low T MOCVD gro~:'n InP / Si(O01) 10000
7500
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(~) 81amInP on Si (001} 3.8° off-cut
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2p.m InP on InP:Fe 5000
T=2K D=O.5W/cm2 2500
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1.36
49
lnP has low residual stress, eth = 6 - 7 X 10 -4. The tilt indicatcs preferential nucleation of type II dislocations with positive tilt component. PL spectra exhibit the smallest peak broadening of 3 meV ever reported to our knowledge for such structures. Etch pit densities of 3 × 10 v cm -2 are observed for a d = 8 / s m lnP layer.
1
1.38
1.40
.42
Energy (eV)
Fig. 3. Comparison of low temperature PL spectra of 8 ~m I n P / S i and 2 ,u,m I n P / ~ n P : F e scaled to same height. The integrated intensity of I n P / I n P is three times larger.
excitation density of 50 m W / c m 2. With arrows at the right border of fig. 2 we have marked for comparison the peak broadening and integrated intensity of an 2 /zm thick undoped InP layer onto l n P : F e substrate. The spectra, scaled to same height, are directly compared in fig. 3. The l n P / S i spectrum is shifted to lower energies due to the tensile thermal stress which is at T = 2 K somewhat larger than at room temperature.
4. Conclusion The structural and optical properties of lnP/Si(001) layers have been investigated. The
Acknowledgements We would like to thank T. Fukunaga (OKI Electric Industries) for generously supplying several Si wafers, R.K. Bauer and P. Fernandez for photoluminescence data and K. Schatke for her expert technical assistance. This work is funded by BMFT under contract No. TK03175.
References [1] M. Grundmann, A. Krost and D. Bimberg, Appl. Phys. Lett. 58 (1991) 284. [2] M. Grundmann, A. Krost and D. Bimberg. J. C~,st. Growth 107 (1991) 494. [3] A. Huber and N.T. Linh, J. Cryst. Growth 29 (1975) 80. [4] R.C. Pond, Crit. Rev. Solid State Mater. Sci. 15 (1989) 44!. [5] N. Otsuka. C. Choi, Y. Nakamura, S. Nagakura. R. Fischer, C.K. Peng and H. Morko~, Appl. Phys. Lett. 49 (1986) 277. [¢~] M. Grundmann. J. ('hrislcn and D. Bimbcrg, Supcrlatt. Micro~,lrucl, • 11991 ) 65.
S u r f a c e science ~5..:..-..
,.-:,.:,.::5
Crystallographic and optical properties of InP/Si(O01) grown by low temperature MOCVD process M. Grundmann, A. Krost, D. Bimberg Technische Universith't Berlin, Institut fiir Festk6rperphysik L Hardenbergstr. 36, W-IO00 Berlin 12, Germany
Received 31 May 1991; accepted for publication 27 June 1991
Growth of antiphase domain free lnP on St(001) is reported using a low temperature metalorganic chemical vapor deposition process without any preannealing of the substrate. The residual stress (typically 6-7 x 10-4), the tilt and the optical properties (best spectral broadening FWHM = 3.0 meV) of the lnP epilayers are characterized.
1. Introduction We have recently p r e s e n t e d a low t e m p e r a t u r e metal organic chemical vapor deposition ( M O C V D ) procedure for antiphase d o m a i n ( A P D ) free growth of InP on Si [1]. This process does not include any high t e m p e r a t u r e annealing, and is thus compatible with optoelectronic integration on St. It is ,~he purpose of this paper to characterize the crystallographic and optical properties of the epitaxial InP layers.
2. Experimental Details about the growth procedure may be found in [1]. We would like to summarize the growth procedure briefly: As substrates we use Si(001) misoriented along [110] with off-cut angles 0 varying from 0.8 ° to 6.0 °. We use a two ,3t~pa ~,IIUWUlprOUCklHIe" after repeated wet chemical oridation and oxide reme"al with 2.5% H F we grow at T>. = 400 ° C a 5.q nm thick InP buf~cr layer using a high V / I l l ratio of 3100 at a growth rate of 0.6 t z m / h . Typical growfl p a r a m e t e r s of the second layer are T = 640 ° C, V / I I I ,'atio of 250 and a growth rate of 2 - 3 t x m / h . We obtain mirror-like surfaces. N o high t e m p e r a t u r e an-
nealing step of the Si substrate prior to epitaxy is used.
3. Charader~zafion On Si with sufficient off-cut we obtain APDfree InP layers (e.g. for 0 = 4 ~' and Tt, - 4 0 0 ° (7) [1,2]. The inhomogeneous broadening of the (004) rocking curve, measured with double crystal X-ray diffraction ( D X D ) , is substantially reduced with increasing layer thickness d; we found F W H M ~ d - ° s [1], indicating that the d o m i n a n t process is a two-dislocation annihilation prccess. A typical value for X-ray diffraction b r o a d e n i n g is F W H M = 258 arcsec for d = 8/.tm. T h e etch pit density revealed by the Huber etch [3] is reduced from over l0 s c m - 2 for d = 1.3 ~tm to 3 x 107 cm -2 for d = 8 g m . With D X D we have m e a s u r e d the residual stress in the l n g and the relative tilt /3 of the ~nP epilaycr with respect to the Si substratc as a function of layer thickness d and off-orientation 0. The results are summarized in fig. 1. The initial stress of about k a / a o = 8% in the InP is compressive. After the growth of some 100 nm this stress is completely relieved plastically via formation of dislocations. During cooling from
11039-6028/92/$05.(1(1 .c 1092 - Elsevier Science Publishers B.V. and Yamad:! Science Foundation. All rights reserved
M. Gmndmann et al. , / L o w T MOCVD grown lnP / Si(O01)
48 ,-.,
1.0 /
I
J
I
tt t i it 1 m
0.5 0.0
300
"6" m t,')
200-
lOO •
i
mm
t 7-. _.
R
m
'
t,
t
,
I
(a)
(c~)
I(b )
(~)
t
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/
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A
,/
,, f
o
,
0
1
,
,
2 3 d(lam)
4
1
t
I
3
5
off-cut (deg)
Fig. 1. Residual in-plane stress (a, c) and tilt (b, d) of the InP epilayer as a function of layer thickness for constant off-cut 0 = 3.8 ° (a, b) and as a function of off-cut for constant layer thickness d = 2.7/xm (c, d).
growth temperature to room temperature after epitaxy a tensile thermal stress eth is generated due to the different thermal expansion coefficients of InP and Si. For layer thickness d >_ 0.7 ~ m we find eth = 6-7 × 10 -4 (fig. la). This value is much smaller than for G~As layers of similar thickness on Si. Fig. lc shows that the residual stress is independent of the off-cut, as expected. The lnP layer is slightly tilted with respect to the Si substrate; the tilt has the same direction as the off-cut ([I-f0]). For constant off-cut the tilt is independent of the layer thickness for d >_ 0.7 g m (,fig. lb); this observation suggests that the tilt is connected with the plastic strain relaxation. Wit': increasing off-cut the tilt shows a linear increase (fig. ld). For the overgrowth of InP on Si one expects a tilt along the opposite direction of the off-cut ([110]) ~theo-- Aa/ao tan 0 (in the case of biatomic steps) [4]; for small angles 0/3th,:,,/00 = --290 arcsec/deg is predicted. Our experimental result of O/3~xp/00 = + 45 arcsec/deg implies that a mechanism exists which accommodates +335 arcsec/deg. Due to the linear dependence of /3 on 0 this mechanism is probably related to the absolute number of steps on the vicinat surface. Jt has bccn shown lot G a A s / S i that the dislocations can have their (110) Burgers vectors in the interface plane (type I, edge dislocation) or inclined to the interface (type II, 60 ° dislocation) [5]. Type I dislocations lead to no tilt of the
overlayer. The observed tilt can be explained by the preferred nucleation of type lI dislocations with Burgers vector b having a positive z-component (b+) compared to those with negative zcomponent (b_). The excess (b+)-(b_) determines the macroscopic tilt; in our case at about every 10th step on the vicinal substrate a b+ dislocation is generated without its b counterpart (independently from the off-cut!). With the reduction of rocking curve broadening also the optical properties are improved with increasing thickness. At low temperature the photoluminescence (PL) spectrum is dominated by shallow donor related luminescence. The peak broadening is reduced and the integrated intensity increases with increasing layer thickness (fig. 2). For large d the spectra of layers with and without APD's do not differ significantly. For small layer thickness the APD's induce larger inhomogeneities. But due to the fact that nonradiative recombination centers are concentrated at the domain boundaries [6], the total quantum efficiency is larger compared to layers without APD's. The smallest PL peak broadening obtained is FWHM = 3.0 meV for d - 8 ~ m and an
InP on $1 (001) • 0.8' off-cut ,~ 3 8 off-cut
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Fig. 2. Photolunfincsccncc peak broadening and integrated intensity :,t T = 2 K for layers with (0 = 0.8 °) and without (0 = 3.8 o ) APD's as a function of !nP I,~yer thickness d. The arrows denote the values for a 2 ~tm | n P layer on InP:Fe.
M. Gmndmann et aL / Low T MOCVD gro~:'n InP / Si(O01) 10000
7500
|
(~) 81amInP on Si (001} 3.8° off-cut
!
(9
,
®
2p.m InP on InP:Fe 5000
T=2K D=O.5W/cm2 2500
'
1.36
49
lnP has low residual stress, eth = 6 - 7 X 10 -4. The tilt indicatcs preferential nucleation of type II dislocations with positive tilt component. PL spectra exhibit the smallest peak broadening of 3 meV ever reported to our knowledge for such structures. Etch pit densities of 3 × 10 v cm -2 are observed for a d = 8 / s m lnP layer.
1
1.38
1.40
.42
Energy (eV)
Fig. 3. Comparison of low temperature PL spectra of 8 ~m I n P / S i and 2 ,u,m I n P / ~ n P : F e scaled to same height. The integrated intensity of I n P / I n P is three times larger.
excitation density of 50 m W / c m 2. With arrows at the right border of fig. 2 we have marked for comparison the peak broadening and integrated intensity of an 2 /zm thick undoped InP layer onto l n P : F e substrate. The spectra, scaled to same height, are directly compared in fig. 3. The l n P / S i spectrum is shifted to lower energies due to the tensile thermal stress which is at T = 2 K somewhat larger than at room temperature.
4. Conclusion The structural and optical properties of lnP/Si(001) layers have been investigated. The
Acknowledgements We would like to thank T. Fukunaga (OKI Electric Industries) for generously supplying several Si wafers, R.K. Bauer and P. Fernandez for photoluminescence data and K. Schatke for her expert technical assistance. This work is funded by BMFT under contract No. TK03175.
References [1] M. Grundmann, A. Krost and D. Bimberg, Appl. Phys. Lett. 58 (1991) 284. [2] M. Grundmann, A. Krost and D. Bimberg. J. C~,st. Growth 107 (1991) 494. [3] A. Huber and N.T. Linh, J. Cryst. Growth 29 (1975) 80. [4] R.C. Pond, Crit. Rev. Solid State Mater. Sci. 15 (1989) 44!. [5] N. Otsuka. C. Choi, Y. Nakamura, S. Nagakura. R. Fischer, C.K. Peng and H. Morko~, Appl. Phys. Lett. 49 (1986) 277. [¢~] M. Grundmann. J. ('hrislcn and D. Bimbcrg, Supcrlatt. Micro~,lrucl, • 11991 ) 65.