- Email: [email protected]
MOVPE grown InP:Yb layers using Yb(IpCp)3 as a new doping source
Journal of Crystal Growth 100 (1990) 467—470 North-Holland
467
MOVPE GROWN InP:Yb LAYERS USING Yb(IpCp)3 AS A NEW DOPING SOURCE J. WEBER, M. MOSER, A. STAPOR and A. HANGLEITER
“,
F. SCHOLZ, G. HORCHER, A. FORCHEL, G. BOHNERT
4. Physikalisches Institut, Universitdt Stuttgart, Pfaffenwaldring 57, D-7000 Stuttgart 80, Fed. Rep. of Germany
and A. HAMMEL
* *
and J. WEIDLEIN
Institut Juir Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-7000 Stuttgart 80, Fed. Rep. of Germany
Received 4 December 1989; manuscript received in final form 6 December 1989
For the Yb-doping of MOVPE grown InP, we have synthesized and used for the first time tris(isopropylcyclopentadienyl)-Yb, Yb(IpCp)3. This compound with its melting point at 47°Ccan be used as a liquid doping source, thus improving the reproducibility of the evaporation compared to the commonly used solid precursors. The grown InP: Yb layers revealed high photoluminescence 3. This indicates intensities the high crystal of thequality Yb 41 of lines, ouralthough samples. the Additionally, Yb concentrations we have grown measured InPby : Yb: SIMS S layers were and onlyInP: in the Yb/InP range :S of multilayer 1017 cm structures with thicknesses between 10 and 100 nm for each layer to study the dependence of the excitation and decay processes on carrier and impurity concentration. The photoluminescence intensity of the 4f emission decreases for high S concentration in InP: Yb : S samples, whereas in the multilayer structures the intensity is the same as in lnP : Yb samples. Based on the assumption of a homogeneous carrier concentration throughout the whole multilayer structure, we believe that a direct interaction between Yb and S atoms is responsible for the decrease in the double-doped single layers. The lifetime of the excited 4f state of Yb3~is 13 fis, regardless of carrier or Yb concentration. For the InP: Yb samples co-doped with 5, a fast nonexponential decay was observed, a further indication of some Yb—S pair interaction.
1. Infroduction The interest in doping rare earth (RE) impurities in 111—V semiconductors is based upon the known sharp 4f emission of the RE3~ions, which is nearly independent of the host crystal. Several groups reported the application of RE doped 111—V semiconductors as near infrared optoelectronic devices [1—3]and proved that the intra-4f-shell emission could be excited electrically and optically via the semiconductor host crystal. To overcome the problems in crystal quality using ion implantation and LPE [4], we have grown InP layers doped with *
Permanent address: Institute of Physics, Polish Academy
* *
of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw Poland. Now at: Department of Physical Chemistry, University of Oslo, P.O. Box 1033, 0372 Oslo, Norway.
0022-0248/90/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
Yb by adduct MOVPE (metal organic vapor phase epitaxy) using different Yb sources. In this paper we discuss the properties of the new tris(isopropylcyclopentadienyl)-Yb, Yb(Ip Cp) 3, compound and its applicability as MOVPE Yb source for the growth of Yb doped InP. The results are compared to those of doping experiment with the solid Yb(MeCp)3 (tris(methylcyclopentadienyl)-Yb) [5]. In order to obtain a better understanding in excitation and decay mechanisms of Yb in InP, we have performed photoluminescence and lifetime experiments. Furthermore, several of the grown samples were co-doped with S to reveal the dependence of these mechanisms on the carrier concentration. A spatial separation of S and Yb was realized by multilayer structures with InP: Yb/InP: S
468
J. Weber et al.
/
MOVPE grown JnP: Yb layers using Yb(JpCp)
7 as a new doping source
layers, to study the influence of carriers on the 4f-luminescence InP : Yb layers. in absence of donor ions in the
InP:3 Yb Typical datas were x 1015a andgrowth. j.t 3000 cm2/V. at 300n K 5 with cm high freeze out ratio of ~3ooK/~77K 3—5. Thus we assume that the incorporated Yb3 ion is either electrically inactive or responsible for a deep level. Recently, Whitney et al. [6] observed in DLTS experiments a level 30 meV below the conduction band correlated to the Yb incorporation. =
=
=
+
2. Growth process Earlier studies with the solid Yb precursor Yb(MeCp) 3 [5] have shown that the doping level could not be controlled because of evaporation rate fluctuations of this compound. Therefore we investigated a new precursor Yb(C3HT-CSH4)3 Yb(IpCp)3, which could be heated and used as a liquid due to its melting point of 47°C. It was synthesized and K(C by the reaction of anhydrous YbC13 3H7—C5H4) in 1,2-dimethoxyethane (DME), according to: 3 K(C3H7—C5H4) + YbC13 Yb(C3H7_C5H4)3 + 3 KC1. (1) The compound was isolated and purified by distillation (160°C,i03 Pa). =
—*
The InP : Yb layers were grown in a conventional MOVPE system with a horizontal reaction chamber with rectangular cross section. Phosphine and trimethylindium—triethylphosphorus were used as P and In sources, respectively. The Yb concentrations were varied via the Yb source ternperature (50—80°C) and the H2 flow through the Yb compound (4—90 SCCM). The growth temperatures ranged between 580 and 670°C. Table 1 shows typical growth parameters for the InP: Yb growth. 3. Results All InP : Yb layers with the new precursor revealed n-type conduction as usual for MOVPE
The layers grown at high bubbler temperatures (70°C)and H2 flow rates (45 SCCM, see table 1) showed strong Yb 4f signals in low temperature photoluminescence, comparable to results from layers doped with Yb(MeCp)3, although SIMS experiments revealed Yb3,concentrations the which are 100oftimes former of about 1017 cm lower than measured in the latter. There are two possible explanations: (a) only a small amount of Yb ions in the InP: Yb layers grown with the solid source is responsible 3~luminescence for the 4f emission, the via or free(b)cxcitons or freeofcarriers excitation the Ybis more efficient in the case of samples grown with Yb(IpCp) 3 in consequence of the better crystal quality. The surface morphology of the InP: Yb layers, grown under the same conditions with the new precursor, is much better than that with the solid source. Partly, this can be explained by the lower Yb incorporation using the liquid source. In all cases, for the same Yb concentrations, we achieved a much better surface morphology of the InP host material and higher photoluminescence intensities with the new liquid precursor. Furthermore, the incorporation rates were highly reproducible, and no memory effect in undoped layers grown directly after Yb doping cxperiments could be detected. In order to study the excitation and decay processes of the radiative Yb transitions at differ-
Table I Growth parameters of InP samples doped with the new Yb precursor; typical data for the doping with Yb(MeCp)7 are given for comparison 7~rowth Th~,hhI~r Source Yb flow Yb No. (°C) (°C) (SCCM) (SIMS) (cm3) Sample Dopant (cm 3) KS175 KS205
Yb Yb, S
670 670
90 90
AM374 AM358
Yb, Yb S
580
70
Yb(MeCp) Yb(MeCp)3 3 Yb(IpCp) Yb(IpCp)3 7
45 45 45 45
19 1.5x10 2 x 1019 7 3 x10’ 3.5x 1017
5
x10~
52 x1015 x 10~ 5 3.6x iO’
J. Weber et a!.
/ MOVPE
grown InP: Yb layers using Yb(IpCp)
ent carrier concentrations, we have grown InP : Yb layers simultaneously doped with sulphur (S). S co-doping enabled us to adjust the carrier concentration in the Yb-doped layers from 5 >< 1015 3, without affecting the Yb incorporation, ascm could be shown by SIMS (table 1). to 5 x iO’~ The 4f emission did not change remarkably for S concentrations up to 1 x iO~cm3, but it decreased drastically for higher S concentrations (fig. 1), although the Yb concentration in these layers was the same as in single-doped layers as evaluated by SIMS. This is a consequence either of the increased number of free carriers or the presence of S atoms in the neighborhood of the Yb3 ± ions. Therefore we separated the S and Yb ions by growing multilayer structures of 20 InP : Yb/ InP: S layers. The thickness L of each layer was varied from 10 to 100 nm. The S concentration in each InP: S layer was 2 x 1018 cm3 and the Yb concentration was 3 X 1017 cm3 (fig. 2). Photoluminescence experiments performed on the thin structures (L 10 nm) revealed the same luminescence intensity of the RE transitions as observed for InP : Yb samples without S and the same Yb concentration. Thus the free carriers, which are thought to penetrate the whole InP: Yb/InP: S superlattice, at least for the thin structure cannot be responsible for the decrease of the Yb3~emission in S-co-doped InP : Yb samples. This in=
102
.
io~
-
InP:Yb:S
-
:7 .~
-
. (‘7 C .~ C
~oo
-
T
=
2 K
-
11019 cm3
-
i0~~-
-
‘‘i 10(6
I 1017
Carrier conc. ~3ooK
469
3 as a new doping source
I 10(8
[cm3]
Fig. 1. Decrease of the Yb luminescence (X = 1002 nm) ~n dependence of the net carrier concentration, achieved by codoping with S.
106
1021
114 In
#~ 391
~
20
InP:Yb/InP:S multilayer d=50
~a. ~o
10
~
1019 ~0
~ ~ ~ 10 102
E
~ 0
1017
250
500
750
10
1250
1500
1750
Depth [nm] Fig. 2. SIMS spectra of an InP : Yb/InP :S superlattice structure. The decrease of the signal dynamics is due to the primary beam induced intermixing effect of SIMS. However, nearly each InP: Yb layer could be resolved, considering the Yb resolution limit of 5 >< 1016 cm
dicates a direct interaction between S and Yb ions in the InP: Yb: S layers, maybe by forming Yb: S complexes during growth.
4. Time dependent photoluminescence measw~ements In our layers grown with the new Yb precursor, we found the same short lifetime of 12—13 p.s (fig. 3) at temperatures below 50 K as reported from several groups for InP : Yb samples grown by LPE and MOVPE using solid sources [7—9]. Thus, it seems to be independent of the Yb concentration and the used Yb source. We assume that the fast decay is closely correlated to an “intrinsic” decay mechanism of the Yb3~center in InP. Measurements of optical gain and quantum efficiency of the Yb3 + are necessary to clarify this behavior and the applicability to optoelectronic devices. S in MOVPE InP: Yb layers led to a fast nonexponential decay in the first ts (fig. 3). For higher S concentrations this nonexponential decay became dominant and only in the long time range were lifetimes of some p.s observed. Such kind of nonexponentiality is known for (D, A) pair recombinations, where the decay depends on the pair distance. This confirms the direct interaction of
470
J. Weber et a!.
/ MOVPE grown InP:
Yb layers using Yb(IpCp)
InP:Yb(:S) =
The independence of the lifetime of about 13 p.s of the excited 4f state on the Yb source material, carrier and Yb concentration, and growth process indicates that this is an “intrinsic” lifetime of 3~in InP. YbThe decay in InP: Yb : S layers was nonexponential in the short time range, whereas the decay in multilayer InP: Yb/InP: S samples was
4.5 K
iO~
-~
monoexponential like in single-doped InP: Yb layers. This result supports the assumption of the existence of an Yb—S interaction, disturbing the excitation and decay of the Yb3 + luminescence.
a: n=5x1015cm3 b: n=5x1016cm3
c: n=2x1017cm3
10
I
0
I
20
40 Time [us]
60
80
Fig. 3. Decay of the Yb line (A = 1002 nm) for MOVPE InP: Yb(: 5) samples with various net carrier concentrations: (a) InP:Yb, n =5x1015 cm3 (300 K); (b) InP:Yb:S, n=5 x1016 cm3 (300 K); (c) InP:Yb:S, n=2X10’7 cm3 (300 K).
Yb and S atoms in the excitation and decay processes as mentioned above.
5. Conclusions We have grown Yb-doped InP samples by MOVPE with the novel liquid doping precursor Yb(IpCp) 3. This compound allows the reproducible growth of InP : Yb epilayers with improved 3± crystal quality. The samples exhibited higher emission intensities at 100 times lower totalYbYb concentrations compared to the layers grown with the solid Yb(MeCp) 3 source. The MOVPE layers consistently exhibited n3 (300 typewithout conductivity in the range of iO’~ cm K) a significant correlation between the incorporated Yb level and the net carrier concentration. The high freeze out ratio of n300K/n77K 3—S is an indication for a deep level connoted to the Yb incorporation. For highly S-co-doped InP : Yb: S layers (n > 1 X 10’3 cm3), we detected a drastic reduction of the Yb3~ photoluminescence intensity, whereas lnP : Yb/InP : S multilayer structures showed strong 4f emission. Therefore, a direct interaction of S and Yb is thought to be responsible for this decrease. =
7 as a new doping source
Acknowledgements The authors would like to thank M.H. Pilkuhn for helpful discussions, B. Notheisen and E. Kuhner for technical assistance. Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. A. Stapor and A. Hammel wish to thank the Alexander von Humbold foundation and the Robert-Bosch Stiftung for financial support, respectively. The authorsfürareAngewandte grateful to H. Ennen, Fraunhofer-Institut Festkorperphysik, Freiburg, for the ion implanted samples used for the calibration of the SIMS setup. References [1] W.T. Tsang and R.A. Logan, Appl. Phys. Letters 49 (1986)
1686. [2] W. Körber, J. Weber, A. Hangleiter and K.W. Benz, J. [3] P.S. Whitney, Crystal Growth K. 79 Uwai, (1986) H. 741.Nakagome and K Takahei, Electron. Letters 24 (1988) 740. [4] H. Nakagome, K. Takahei and Y. Homma, J. Crystal Growth 85 (1987) 345. [5] J. Weber, A. A.Forchel, Molassioti, M. Moser, Stapor, G. Hörcher, A. Hammel, G.A. Laube andF.J.Scholz, Weidlein, Appl. Phys. Letters 53 (1988) 2525. [6] P.S. Whitney, K. Uwai, H. Nakagome and K. Takahei, Appl. Phys. Letters 53 (1988) 2074. [7] P.B. Klein, Mater. Res. Soc. Symp. Proc. 104 (1988) 437. [8] W. Khrber (1988) 114. and A. Hangleiter, AppI. Phys. Letters 52 [9] K. Takahei, K. Uwai and H. Nakagome, J. Luminescence 40&41 (1988) 901.
467
MOVPE GROWN InP:Yb LAYERS USING Yb(IpCp)3 AS A NEW DOPING SOURCE J. WEBER, M. MOSER, A. STAPOR and A. HANGLEITER
“,
F. SCHOLZ, G. HORCHER, A. FORCHEL, G. BOHNERT
4. Physikalisches Institut, Universitdt Stuttgart, Pfaffenwaldring 57, D-7000 Stuttgart 80, Fed. Rep. of Germany
and A. HAMMEL
* *
and J. WEIDLEIN
Institut Juir Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-7000 Stuttgart 80, Fed. Rep. of Germany
Received 4 December 1989; manuscript received in final form 6 December 1989
For the Yb-doping of MOVPE grown InP, we have synthesized and used for the first time tris(isopropylcyclopentadienyl)-Yb, Yb(IpCp)3. This compound with its melting point at 47°Ccan be used as a liquid doping source, thus improving the reproducibility of the evaporation compared to the commonly used solid precursors. The grown InP: Yb layers revealed high photoluminescence 3. This indicates intensities the high crystal of thequality Yb 41 of lines, ouralthough samples. the Additionally, Yb concentrations we have grown measured InPby : Yb: SIMS S layers were and onlyInP: in the Yb/InP range :S of multilayer 1017 cm structures with thicknesses between 10 and 100 nm for each layer to study the dependence of the excitation and decay processes on carrier and impurity concentration. The photoluminescence intensity of the 4f emission decreases for high S concentration in InP: Yb : S samples, whereas in the multilayer structures the intensity is the same as in lnP : Yb samples. Based on the assumption of a homogeneous carrier concentration throughout the whole multilayer structure, we believe that a direct interaction between Yb and S atoms is responsible for the decrease in the double-doped single layers. The lifetime of the excited 4f state of Yb3~is 13 fis, regardless of carrier or Yb concentration. For the InP: Yb samples co-doped with 5, a fast nonexponential decay was observed, a further indication of some Yb—S pair interaction.
1. Infroduction The interest in doping rare earth (RE) impurities in 111—V semiconductors is based upon the known sharp 4f emission of the RE3~ions, which is nearly independent of the host crystal. Several groups reported the application of RE doped 111—V semiconductors as near infrared optoelectronic devices [1—3]and proved that the intra-4f-shell emission could be excited electrically and optically via the semiconductor host crystal. To overcome the problems in crystal quality using ion implantation and LPE [4], we have grown InP layers doped with *
Permanent address: Institute of Physics, Polish Academy
* *
of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw Poland. Now at: Department of Physical Chemistry, University of Oslo, P.O. Box 1033, 0372 Oslo, Norway.
0022-0248/90/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
Yb by adduct MOVPE (metal organic vapor phase epitaxy) using different Yb sources. In this paper we discuss the properties of the new tris(isopropylcyclopentadienyl)-Yb, Yb(Ip Cp) 3, compound and its applicability as MOVPE Yb source for the growth of Yb doped InP. The results are compared to those of doping experiment with the solid Yb(MeCp)3 (tris(methylcyclopentadienyl)-Yb) [5]. In order to obtain a better understanding in excitation and decay mechanisms of Yb in InP, we have performed photoluminescence and lifetime experiments. Furthermore, several of the grown samples were co-doped with S to reveal the dependence of these mechanisms on the carrier concentration. A spatial separation of S and Yb was realized by multilayer structures with InP: Yb/InP: S
468
J. Weber et al.
/
MOVPE grown JnP: Yb layers using Yb(JpCp)
7 as a new doping source
layers, to study the influence of carriers on the 4f-luminescence InP : Yb layers. in absence of donor ions in the
InP:3 Yb Typical datas were x 1015a andgrowth. j.t 3000 cm2/V. at 300n K 5 with cm high freeze out ratio of ~3ooK/~77K 3—5. Thus we assume that the incorporated Yb3 ion is either electrically inactive or responsible for a deep level. Recently, Whitney et al. [6] observed in DLTS experiments a level 30 meV below the conduction band correlated to the Yb incorporation. =
=
=
+
2. Growth process Earlier studies with the solid Yb precursor Yb(MeCp) 3 [5] have shown that the doping level could not be controlled because of evaporation rate fluctuations of this compound. Therefore we investigated a new precursor Yb(C3HT-CSH4)3 Yb(IpCp)3, which could be heated and used as a liquid due to its melting point of 47°C. It was synthesized and K(C by the reaction of anhydrous YbC13 3H7—C5H4) in 1,2-dimethoxyethane (DME), according to: 3 K(C3H7—C5H4) + YbC13 Yb(C3H7_C5H4)3 + 3 KC1. (1) The compound was isolated and purified by distillation (160°C,i03 Pa). =
—*
The InP : Yb layers were grown in a conventional MOVPE system with a horizontal reaction chamber with rectangular cross section. Phosphine and trimethylindium—triethylphosphorus were used as P and In sources, respectively. The Yb concentrations were varied via the Yb source ternperature (50—80°C) and the H2 flow through the Yb compound (4—90 SCCM). The growth temperatures ranged between 580 and 670°C. Table 1 shows typical growth parameters for the InP: Yb growth. 3. Results All InP : Yb layers with the new precursor revealed n-type conduction as usual for MOVPE
The layers grown at high bubbler temperatures (70°C)and H2 flow rates (45 SCCM, see table 1) showed strong Yb 4f signals in low temperature photoluminescence, comparable to results from layers doped with Yb(MeCp)3, although SIMS experiments revealed Yb3,concentrations the which are 100oftimes former of about 1017 cm lower than measured in the latter. There are two possible explanations: (a) only a small amount of Yb ions in the InP: Yb layers grown with the solid source is responsible 3~luminescence for the 4f emission, the via or free(b)cxcitons or freeofcarriers excitation the Ybis more efficient in the case of samples grown with Yb(IpCp) 3 in consequence of the better crystal quality. The surface morphology of the InP: Yb layers, grown under the same conditions with the new precursor, is much better than that with the solid source. Partly, this can be explained by the lower Yb incorporation using the liquid source. In all cases, for the same Yb concentrations, we achieved a much better surface morphology of the InP host material and higher photoluminescence intensities with the new liquid precursor. Furthermore, the incorporation rates were highly reproducible, and no memory effect in undoped layers grown directly after Yb doping cxperiments could be detected. In order to study the excitation and decay processes of the radiative Yb transitions at differ-
Table I Growth parameters of InP samples doped with the new Yb precursor; typical data for the doping with Yb(MeCp)7 are given for comparison 7~rowth Th~,hhI~r Source Yb flow Yb No. (°C) (°C) (SCCM) (SIMS) (cm3) Sample Dopant (cm 3) KS175 KS205
Yb Yb, S
670 670
90 90
AM374 AM358
Yb, Yb S
580
70
Yb(MeCp) Yb(MeCp)3 3 Yb(IpCp) Yb(IpCp)3 7
45 45 45 45
19 1.5x10 2 x 1019 7 3 x10’ 3.5x 1017
5
x10~
52 x1015 x 10~ 5 3.6x iO’
J. Weber et a!.
/ MOVPE
grown InP: Yb layers using Yb(IpCp)
ent carrier concentrations, we have grown InP : Yb layers simultaneously doped with sulphur (S). S co-doping enabled us to adjust the carrier concentration in the Yb-doped layers from 5 >< 1015 3, without affecting the Yb incorporation, ascm could be shown by SIMS (table 1). to 5 x iO’~ The 4f emission did not change remarkably for S concentrations up to 1 x iO~cm3, but it decreased drastically for higher S concentrations (fig. 1), although the Yb concentration in these layers was the same as in single-doped layers as evaluated by SIMS. This is a consequence either of the increased number of free carriers or the presence of S atoms in the neighborhood of the Yb3 ± ions. Therefore we separated the S and Yb ions by growing multilayer structures of 20 InP : Yb/ InP: S layers. The thickness L of each layer was varied from 10 to 100 nm. The S concentration in each InP: S layer was 2 x 1018 cm3 and the Yb concentration was 3 X 1017 cm3 (fig. 2). Photoluminescence experiments performed on the thin structures (L 10 nm) revealed the same luminescence intensity of the RE transitions as observed for InP : Yb samples without S and the same Yb concentration. Thus the free carriers, which are thought to penetrate the whole InP: Yb/InP: S superlattice, at least for the thin structure cannot be responsible for the decrease of the Yb3~emission in S-co-doped InP : Yb samples. This in=
102
.
io~
-
InP:Yb:S
-
:7 .~
-
. (‘7 C .~ C
~oo
-
T
=
2 K
-
11019 cm3
-
i0~~-
-
‘‘i 10(6
I 1017
Carrier conc. ~3ooK
469
3 as a new doping source
I 10(8
[cm3]
Fig. 1. Decrease of the Yb luminescence (X = 1002 nm) ~n dependence of the net carrier concentration, achieved by codoping with S.
106
1021
114 In
#~ 391
~
20
InP:Yb/InP:S multilayer d=50
~a. ~o
10
~
1019 ~0
~ ~ ~ 10 102
E
~ 0
1017
250
500
750
10
1250
1500
1750
Depth [nm] Fig. 2. SIMS spectra of an InP : Yb/InP :S superlattice structure. The decrease of the signal dynamics is due to the primary beam induced intermixing effect of SIMS. However, nearly each InP: Yb layer could be resolved, considering the Yb resolution limit of 5 >< 1016 cm
dicates a direct interaction between S and Yb ions in the InP: Yb: S layers, maybe by forming Yb: S complexes during growth.
4. Time dependent photoluminescence measw~ements In our layers grown with the new Yb precursor, we found the same short lifetime of 12—13 p.s (fig. 3) at temperatures below 50 K as reported from several groups for InP : Yb samples grown by LPE and MOVPE using solid sources [7—9]. Thus, it seems to be independent of the Yb concentration and the used Yb source. We assume that the fast decay is closely correlated to an “intrinsic” decay mechanism of the Yb3~center in InP. Measurements of optical gain and quantum efficiency of the Yb3 + are necessary to clarify this behavior and the applicability to optoelectronic devices. S in MOVPE InP: Yb layers led to a fast nonexponential decay in the first ts (fig. 3). For higher S concentrations this nonexponential decay became dominant and only in the long time range were lifetimes of some p.s observed. Such kind of nonexponentiality is known for (D, A) pair recombinations, where the decay depends on the pair distance. This confirms the direct interaction of
470
J. Weber et a!.
/ MOVPE grown InP:
Yb layers using Yb(IpCp)
InP:Yb(:S) =
The independence of the lifetime of about 13 p.s of the excited 4f state on the Yb source material, carrier and Yb concentration, and growth process indicates that this is an “intrinsic” lifetime of 3~in InP. YbThe decay in InP: Yb : S layers was nonexponential in the short time range, whereas the decay in multilayer InP: Yb/InP: S samples was
4.5 K
iO~
-~
monoexponential like in single-doped InP: Yb layers. This result supports the assumption of the existence of an Yb—S interaction, disturbing the excitation and decay of the Yb3 + luminescence.
a: n=5x1015cm3 b: n=5x1016cm3
c: n=2x1017cm3
10
I
0
I
20
40 Time [us]
60
80
Fig. 3. Decay of the Yb line (A = 1002 nm) for MOVPE InP: Yb(: 5) samples with various net carrier concentrations: (a) InP:Yb, n =5x1015 cm3 (300 K); (b) InP:Yb:S, n=5 x1016 cm3 (300 K); (c) InP:Yb:S, n=2X10’7 cm3 (300 K).
Yb and S atoms in the excitation and decay processes as mentioned above.
5. Conclusions We have grown Yb-doped InP samples by MOVPE with the novel liquid doping precursor Yb(IpCp) 3. This compound allows the reproducible growth of InP : Yb epilayers with improved 3± crystal quality. The samples exhibited higher emission intensities at 100 times lower totalYbYb concentrations compared to the layers grown with the solid Yb(MeCp) 3 source. The MOVPE layers consistently exhibited n3 (300 typewithout conductivity in the range of iO’~ cm K) a significant correlation between the incorporated Yb level and the net carrier concentration. The high freeze out ratio of n300K/n77K 3—S is an indication for a deep level connoted to the Yb incorporation. For highly S-co-doped InP : Yb: S layers (n > 1 X 10’3 cm3), we detected a drastic reduction of the Yb3~ photoluminescence intensity, whereas lnP : Yb/InP : S multilayer structures showed strong 4f emission. Therefore, a direct interaction of S and Yb is thought to be responsible for this decrease. =
7 as a new doping source
Acknowledgements The authors would like to thank M.H. Pilkuhn for helpful discussions, B. Notheisen and E. Kuhner for technical assistance. Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. A. Stapor and A. Hammel wish to thank the Alexander von Humbold foundation and the Robert-Bosch Stiftung for financial support, respectively. The authorsfürareAngewandte grateful to H. Ennen, Fraunhofer-Institut Festkorperphysik, Freiburg, for the ion implanted samples used for the calibration of the SIMS setup. References [1] W.T. Tsang and R.A. Logan, Appl. Phys. Letters 49 (1986)
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