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Segregation coefficients of selected impurities in ZnSe grown by LPE
Journal of Crystal Growth 59 (1982) 649—650 North-Holland Publishing Company
649
LETFER TO THE EDITORS SEGREGATION COEFFICIENTS OF SELECTED IMPURITIES IN ZnSe GROWN BY LPE T.F. McGEE III and C. WERKHOVEN
*
Philips Laboratories, 345 Scarborough Road, Briarcliff Manor, New York 10510, USA
and J. JANSEN Philips Research Laboratories, 5600 MD Eindhoven, The Netherlands Received 30 June 1982
Layers of ZnSe were grown by liquid phase epitaxy using a Sn solvent in the temperature range 950—840°C and a cooling rate 1 °C/min.The segregation coefficients of selected impurities were then determined by using the weight amounts of the constituents added and the concentration in the layer as determined by laser mass spectrometric analysis.
The Il—VI compound semiconductor ZnSe may be useful for electroluminescent devices and blue LED’s. To be able to make such devices it is necessary to control impurities since they can effect both the electrical and optical properties of the material. One preferred method for controllably growing thin layers is liquid phase epitaxy (LPE) of which very little is known for ZnSe. In controlling impurities, knowledge of their segregation coefficients is beneficial, and the segregation coefficients of selected impurities are reported here, The growth system consisted of a multichamber graphite boat with a graphite slider which enabled the wafer to slide under the melt. The furnace was a Transtemp transparent gold reflector furnace whose winding was replaced with 1 mm Pt/lO%Rh wire for purity reasons. A quartz tube was inserted through the furnace and connected to a gas manifold to provide an H 2 atmosphere for growth. The other end of the tube was enclosed in a stainless steel dry box with an N2 atmosphere to provide a dry atmosphere for the growth preparation. Previous undoped layers grown from this system have *
Present address: Philips Research Laboratories, 5600 MD Eindhoven, The Netherlands.
0022-0248/82/0000—0000/$02.75
©
total donor and acceptor concentrations of less than 5 X 1O’6/cm3 [1,2]. The substrates were cut from ultra-high purity ZnSe boules (Eagle Picher, Inc.). The highest impurity concentration observed was 0.5 ppm of Cr by laser mass spectrometric analysis [3]. The substrates were nominally (111 }A oriented and the surface was bromine—methanol polished. The substrates were cleaved into wafers approximately 1 cm2. Before growth, the wafers were cleaned in hot solvents followed by etching in 45°KOH. Table I Amounts of constituents added to the melt
_____________________________________________ wt impunty (mg
wt Zn (mg)
wt SE (mg)
wt Sn melt (g)
Al In Fe Si Ga
0.4 0.48 0.57 0.
59.9 60.5 61.0 60.2
60.0 59.7 60.6 59.2
0142
6019
5919
10 10 10 10 10
Cr Cu
0.77 0.51
60.6 61.2
60.7 61.3
10 10
1982 North-Holland
650
T F. McGee IJI et al.
/
Segregation coefficients of selected impurities in ZnSe
Table 2 Analysis results and segregation coefficients
__________________________________________________
Al In Fe Si Mn Ga Cr Cu
CL°~
C
0.02 0.005 0.01 0.023 0.013 0.007 0.02 0.01
0.16 0.05 0.004 0.003 5.3 0.001 0.03 0.0004
5~
k
8 10 0.4 0.1 400 0.1 1.5 0.04
___________________________________________ ~ CL represents the mole percent of the impurity in the liquid, b
c~represents the
mole percent of the impurity in the solid,
The solvent for the growths was Sn into which Zn, Se and the dopant of interest were dissolved (table 1). In all cases the starting temperature was 950°C and the cooling rate was 1°C/mm. The final temperature was 850°Cexcept for Fe and Cr where the final temperature was 840°C. After growth, all samples were rapidly cooled to room temperature in an H2 atmosphere. It is probable that very-near equilibrium growth conditions were attained since the final temperature was far below the liquidus temperature (900°C)[4] and a cooling rate of 1°C/mm. The layers grown were typically 10 ~tm thick and had surface morphology typical of GaAs grown by LPE.
After growth, the layers were analyzed using laser mass spectrometric analysis. These results and the calculated segregation coefficients are shown in table 2. As is evident from table 2, most of the elements investigated have moderate segregation coefficients and with the use of high purity starting materials should be easily controllable as background impurities. Copper appears to have a low segregation coefficient. This is probably due to its high diffusion rate as it can diffuse away from the layer into the substrate upon cooling. Of the ones with high segregation coefficients, aluminum and indium are donors and must be carefully controlled. Manganese, however, is generally regarded as an isoelectronic impurity and should not present a problem with electrical properties. Even though these results were obtained from a tin solvent only, they should represent a general trend for impurity segregation using other solvents for Il—VI compounds.
References [I] B.J. Fitzpatrick, C. Werkhoven, T.F. McGee, P. Harnack, S.P. Herko, R.N. Bhargava and P.J. Dean, IEEE Trans. Electron Devices ED-28 (1981) 440. [2] C. Werkhoven, F.J. Fitzpatrick, S.P. Herko and R N. Bhargava, AppI. Phys. Letters 30(1981) 540. [31J.A. Jansen and A.W. Witmer, Spectrochim. Acta, in press. [4] M. Rubenstein, J. Crystal Growth 3/4 (1968) 309.
649
LETFER TO THE EDITORS SEGREGATION COEFFICIENTS OF SELECTED IMPURITIES IN ZnSe GROWN BY LPE T.F. McGEE III and C. WERKHOVEN
*
Philips Laboratories, 345 Scarborough Road, Briarcliff Manor, New York 10510, USA
and J. JANSEN Philips Research Laboratories, 5600 MD Eindhoven, The Netherlands Received 30 June 1982
Layers of ZnSe were grown by liquid phase epitaxy using a Sn solvent in the temperature range 950—840°C and a cooling rate 1 °C/min.The segregation coefficients of selected impurities were then determined by using the weight amounts of the constituents added and the concentration in the layer as determined by laser mass spectrometric analysis.
The Il—VI compound semiconductor ZnSe may be useful for electroluminescent devices and blue LED’s. To be able to make such devices it is necessary to control impurities since they can effect both the electrical and optical properties of the material. One preferred method for controllably growing thin layers is liquid phase epitaxy (LPE) of which very little is known for ZnSe. In controlling impurities, knowledge of their segregation coefficients is beneficial, and the segregation coefficients of selected impurities are reported here, The growth system consisted of a multichamber graphite boat with a graphite slider which enabled the wafer to slide under the melt. The furnace was a Transtemp transparent gold reflector furnace whose winding was replaced with 1 mm Pt/lO%Rh wire for purity reasons. A quartz tube was inserted through the furnace and connected to a gas manifold to provide an H 2 atmosphere for growth. The other end of the tube was enclosed in a stainless steel dry box with an N2 atmosphere to provide a dry atmosphere for the growth preparation. Previous undoped layers grown from this system have *
Present address: Philips Research Laboratories, 5600 MD Eindhoven, The Netherlands.
0022-0248/82/0000—0000/$02.75
©
total donor and acceptor concentrations of less than 5 X 1O’6/cm3 [1,2]. The substrates were cut from ultra-high purity ZnSe boules (Eagle Picher, Inc.). The highest impurity concentration observed was 0.5 ppm of Cr by laser mass spectrometric analysis [3]. The substrates were nominally (111 }A oriented and the surface was bromine—methanol polished. The substrates were cleaved into wafers approximately 1 cm2. Before growth, the wafers were cleaned in hot solvents followed by etching in 45°KOH. Table I Amounts of constituents added to the melt
_____________________________________________ wt impunty (mg
wt Zn (mg)
wt SE (mg)
wt Sn melt (g)
Al In Fe Si Ga
0.4 0.48 0.57 0.
59.9 60.5 61.0 60.2
60.0 59.7 60.6 59.2
0142
6019
5919
10 10 10 10 10
Cr Cu
0.77 0.51
60.6 61.2
60.7 61.3
10 10
1982 North-Holland
650
T F. McGee IJI et al.
/
Segregation coefficients of selected impurities in ZnSe
Table 2 Analysis results and segregation coefficients
__________________________________________________
Al In Fe Si Mn Ga Cr Cu
CL°~
C
0.02 0.005 0.01 0.023 0.013 0.007 0.02 0.01
0.16 0.05 0.004 0.003 5.3 0.001 0.03 0.0004
5~
k
8 10 0.4 0.1 400 0.1 1.5 0.04
___________________________________________ ~ CL represents the mole percent of the impurity in the liquid, b
c~represents the
mole percent of the impurity in the solid,
The solvent for the growths was Sn into which Zn, Se and the dopant of interest were dissolved (table 1). In all cases the starting temperature was 950°C and the cooling rate was 1°C/mm. The final temperature was 850°Cexcept for Fe and Cr where the final temperature was 840°C. After growth, all samples were rapidly cooled to room temperature in an H2 atmosphere. It is probable that very-near equilibrium growth conditions were attained since the final temperature was far below the liquidus temperature (900°C)[4] and a cooling rate of 1°C/mm. The layers grown were typically 10 ~tm thick and had surface morphology typical of GaAs grown by LPE.
After growth, the layers were analyzed using laser mass spectrometric analysis. These results and the calculated segregation coefficients are shown in table 2. As is evident from table 2, most of the elements investigated have moderate segregation coefficients and with the use of high purity starting materials should be easily controllable as background impurities. Copper appears to have a low segregation coefficient. This is probably due to its high diffusion rate as it can diffuse away from the layer into the substrate upon cooling. Of the ones with high segregation coefficients, aluminum and indium are donors and must be carefully controlled. Manganese, however, is generally regarded as an isoelectronic impurity and should not present a problem with electrical properties. Even though these results were obtained from a tin solvent only, they should represent a general trend for impurity segregation using other solvents for Il—VI compounds.
References [I] B.J. Fitzpatrick, C. Werkhoven, T.F. McGee, P. Harnack, S.P. Herko, R.N. Bhargava and P.J. Dean, IEEE Trans. Electron Devices ED-28 (1981) 440. [2] C. Werkhoven, F.J. Fitzpatrick, S.P. Herko and R N. Bhargava, AppI. Phys. Letters 30(1981) 540. [31J.A. Jansen and A.W. Witmer, Spectrochim. Acta, in press. [4] M. Rubenstein, J. Crystal Growth 3/4 (1968) 309.