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Subnanosecond carriers lifetime measurement in 1.3μ InGaAsP
500
Journal of luminescence 31 & 32(1984)500-502 North-Ilolland, Amsterdam
SUBNANOSECOND CARRIERS LIFETIME MEASUREMENT IN
1.3ii InGaAsP
Bernard SERMAGE and dean Louis BENCHIMDL Laboratoire de Bagneux, CNET, 196 rue de Paris, 92220
BAGNEUX
—
FRANCE
and Jonathan Paul HERITAGE Bell Laboratories, Crawford Corner Road, Holmdel
,
New Jersey 07733
-
U.S.A
The Auger recombinaison coefficient has been determined in 1.31-1 InGaA5P at different temperatures by observation of the luminescence decay following a loops pulse excitation. The Auger coefficient (Ca=2.6 10—29cm6s-1) does not increase with temperature which leads to an Auger limited T 0 value of 121K for 1.3p InGaAsP lasers. 1. INTRODUCTION InGaA5P lasers and LED are important light sources for fiber optic communications in l.2—1.6p spectral range. The utilisation of these lasers is actually disturbed by the unusually strong temperature dependence of the threshold current which is not well understood’. Auger recombination is one of several proposed explanations for this coefficientdependence has been recently determi2’3.effect’. However Auger the temperature of the Auger coened at room fficient has temperature never been studied experimentally though this is useful for the determination of the temperature variation of threshold current in InGaA5P lasers. 2. EXPERIMENTAL PROCEDURE The experiment consists in observing with a very fast photodiode (response time l5ops) the decay luminescence of an 1.3p InGaA5P sample excited by a 1.061-i mode locked YAG laser. The delay between two pulses is 250 ns. The laser beam is focalised with a microscope objective on the sample whose temperature can be varied with a Peltier device or a cryostat. We have studied different samples with quartenary layer thicknesses varying between 0.33-i and l.6p covered with an InP cap layer. The overall resolution of the system is 150 ps. We have measured with pinholes the diameter of the beam at the position where we place the sample. The density of carriers is calculated by writing that each absorbed photon creates an electron—hole pair. By varying the laser intensity, we can thus vary the carriers density in the InGaAsP layer between 4.1016 and 2.1O’9cm3 The luminescence decay time is obtained by the tangent at t=O of the luminescence decay curves. Since the luminescence intensity L is not propor— tionnal to the carriers density n, the carriers lifetime is given by 0022—23 I 3/84/$03 00 © Elsevier Science Publishers By. (North-Holland Physics Publishing Division)
B. Sermage et al.
1
dLogn dLogL
— -
1 f~
—
/ Subnanosecond carriers lifetime measurement 1
.
501
1
-
Tr has been calculated using where Y=dLog(1/r~)/dLogn. The radiative lifetime Fermi golden rule as in ref.4. We suppose k conservation and take into account the non parabolicity of the bands following Kane model. The Kane parameters are deduced from the values inF: E =0,953eV, A 0=O,25eV, me=O,0566, mhh=O,465, mhl= 5 g 0.074 .The matrix element is deduced thecarriers absorption coefficient at 1.069: 4cm~.The dependence of l/Tr from versus density and temperature a=1.6 1O can be seen on fig.1. At low and intermediate density (n< 2.lO18cm3), a good approximation is given by the following expression: 1
=
Brn
+
Cm2
where Br=l•92 1OlO(300/T)LScm3s’ and Cr=_4•7 1O29(3OO/T)3cm6s~. From these curves, we can calculate~andthen using eq.1 the carriers life time for each experimental value of the luminescence decay timetL. 3. RESULTS AND DISCUSSIONS At low carriers density, (n<1018cm3) the l/T curves follow the theoretical radiative ones. At 32 and 82K we obs-
i~~-
erve a heating of the carriers (the
w
curves are close to the 601< and lOOK theoretical radiative ones). At high
~
carriers density(n>1018 cm3),1/T in-
~
creases more rapidly than l/~. At low temperature (32K, 82K and 200K) we are
~
200K
i~1O9 -
,‘r..’
~
not sure on the origin of this effect: Auger mechanism or stimul ated recombi nation. At 28lKand 346K, we have checked that stimulated recombination was negligible by comparing the results obtained with two diameters of the ex—
Experimental curves of the inverse lifetime (full line) and calculated ~(~Sht~ inverse radiative ii-
cited area( 15.59 and 9.o)and different
of carriers density
1016
1017
1019
CARRIERS DENSITY (cm-3)
thicknesses of the quaternary layer. The life times obtained in these different cases fall on the same curve. As can be seen on fig.2, l/Ta=l/T_l/Tr points are rather well fitted by the usual square law caracteristic of an Auger process: 1/Ta=Can2• The Auger coefficient Ca is found to be equal to 2.6 1O29cm6s~at both temperatures (281K and 3461<). This value is in agreement with ref.3 (Ca=l•5 1029cm6s1) and with
502
B. Serorage ci aL/Strbira,tusroiul arrir’r.s
li/r’tuite 1/tea\tsrr’nU ti
lnGaAsP
/
//
3~68
~Q8
CARRIERS DENSITY (cm~)
10
10
1018
CARRIERS DENSITV(cm
101~ 1)
FIGURE 2 Inverse carriers lifetime in 1.39 InGaA5P. The crosses are the experimental inverse lifetimes. The dashed line is the calculated inverse radiative lifetime. The open circles are obtained by substracting the dashed line to the crosses and represent the non radiative part of the recombination. The dashed dotted line is a Can2 curve with Ca=2.6 10—29cm6s—1. The full line is the sum of the dashed and the dashed dotted line. 6 (Ca=2•7 1029cm6s~) and is lower than previous recent theoretical calculations measurements and calculations. Furthermore it shows that Auger coefficient does not increase with temperature as it was thought peviously. Anyhow, using the value of the Auger coefficient we have measured and the fact it is constant around room temperature, we can calculate the To value for 1.3p InGaA5P lasers taking into account a recycling of the photons of 1.5 in the active layer. We find T 0=121K (a value larger than the one observed on lasers:5O—90K) which shows that Auger recombination is not sufficient to explain these small T0 values. REFERENCES 1) Y. Horikoshi in : 379—411 InGaAsP alloy semiconductors, ed. T.P. Pearsall (J. 1982)H.d. pp. Eichler, d.P. Heritage, R.J. Nelson and N.K. Dutta, Appl. 2) B.Wiley, Semmage, Phys. Lett. 42, 259 (1983) 3) E. Wintner and E.P. Ippen, Appl. Phys. Lett. 44, 999 (1984) 4) H.L. Casey and M.B. Panish, Heterostructure lasers, Academic press, New York 1978, p.129 5) T.P. Pearsall in : InGaA5P alloy semiconductors, ed. T.P. Pearsall (J. Wiley, 1982) pp. 295—312 6) M. Takeshima, Phys rev.B, 29, 1993 (1984)
Journal of luminescence 31 & 32(1984)500-502 North-Ilolland, Amsterdam
SUBNANOSECOND CARRIERS LIFETIME MEASUREMENT IN
1.3ii InGaAsP
Bernard SERMAGE and dean Louis BENCHIMDL Laboratoire de Bagneux, CNET, 196 rue de Paris, 92220
BAGNEUX
—
FRANCE
and Jonathan Paul HERITAGE Bell Laboratories, Crawford Corner Road, Holmdel
,
New Jersey 07733
-
U.S.A
The Auger recombinaison coefficient has been determined in 1.31-1 InGaA5P at different temperatures by observation of the luminescence decay following a loops pulse excitation. The Auger coefficient (Ca=2.6 10—29cm6s-1) does not increase with temperature which leads to an Auger limited T 0 value of 121K for 1.3p InGaAsP lasers. 1. INTRODUCTION InGaA5P lasers and LED are important light sources for fiber optic communications in l.2—1.6p spectral range. The utilisation of these lasers is actually disturbed by the unusually strong temperature dependence of the threshold current which is not well understood’. Auger recombination is one of several proposed explanations for this coefficientdependence has been recently determi2’3.effect’. However Auger the temperature of the Auger coened at room fficient has temperature never been studied experimentally though this is useful for the determination of the temperature variation of threshold current in InGaA5P lasers. 2. EXPERIMENTAL PROCEDURE The experiment consists in observing with a very fast photodiode (response time l5ops) the decay luminescence of an 1.3p InGaA5P sample excited by a 1.061-i mode locked YAG laser. The delay between two pulses is 250 ns. The laser beam is focalised with a microscope objective on the sample whose temperature can be varied with a Peltier device or a cryostat. We have studied different samples with quartenary layer thicknesses varying between 0.33-i and l.6p covered with an InP cap layer. The overall resolution of the system is 150 ps. We have measured with pinholes the diameter of the beam at the position where we place the sample. The density of carriers is calculated by writing that each absorbed photon creates an electron—hole pair. By varying the laser intensity, we can thus vary the carriers density in the InGaAsP layer between 4.1016 and 2.1O’9cm3 The luminescence decay time is obtained by the tangent at t=O of the luminescence decay curves. Since the luminescence intensity L is not propor— tionnal to the carriers density n, the carriers lifetime is given by 0022—23 I 3/84/$03 00 © Elsevier Science Publishers By. (North-Holland Physics Publishing Division)
B. Sermage et al.
1
dLogn dLogL
— -
1 f~
—
/ Subnanosecond carriers lifetime measurement 1
.
501
1
-
Tr has been calculated using where Y=dLog(1/r~)/dLogn. The radiative lifetime Fermi golden rule as in ref.4. We suppose k conservation and take into account the non parabolicity of the bands following Kane model. The Kane parameters are deduced from the values inF: E =0,953eV, A 0=O,25eV, me=O,0566, mhh=O,465, mhl= 5 g 0.074 .The matrix element is deduced thecarriers absorption coefficient at 1.069: 4cm~.The dependence of l/Tr from versus density and temperature a=1.6 1O can be seen on fig.1. At low and intermediate density (n< 2.lO18cm3), a good approximation is given by the following expression: 1
=
Brn
+
Cm2
where Br=l•92 1OlO(300/T)LScm3s’ and Cr=_4•7 1O29(3OO/T)3cm6s~. From these curves, we can calculate~andthen using eq.1 the carriers life time for each experimental value of the luminescence decay timetL. 3. RESULTS AND DISCUSSIONS At low carriers density, (n<1018cm3) the l/T curves follow the theoretical radiative ones. At 32 and 82K we obs-
i~~-
erve a heating of the carriers (the
w
curves are close to the 601< and lOOK theoretical radiative ones). At high
~
carriers density(n>1018 cm3),1/T in-
~
creases more rapidly than l/~. At low temperature (32K, 82K and 200K) we are
~
200K
i~1O9 -
,‘r..’
~
not sure on the origin of this effect: Auger mechanism or stimul ated recombi nation. At 28lKand 346K, we have checked that stimulated recombination was negligible by comparing the results obtained with two diameters of the ex—
Experimental curves of the inverse lifetime (full line) and calculated ~(~Sht~ inverse radiative ii-
cited area( 15.59 and 9.o)and different
of carriers density
1016
1017
1019
CARRIERS DENSITY (cm-3)
thicknesses of the quaternary layer. The life times obtained in these different cases fall on the same curve. As can be seen on fig.2, l/Ta=l/T_l/Tr points are rather well fitted by the usual square law caracteristic of an Auger process: 1/Ta=Can2• The Auger coefficient Ca is found to be equal to 2.6 1O29cm6s~at both temperatures (281K and 3461<). This value is in agreement with ref.3 (Ca=l•5 1029cm6s1) and with
502
B. Serorage ci aL/Strbira,tusroiul arrir’r.s
li/r’tuite 1/tea\tsrr’nU ti
lnGaAsP
/
//
3~68
~Q8
CARRIERS DENSITY (cm~)
10
10
1018
CARRIERS DENSITV(cm
101~ 1)
FIGURE 2 Inverse carriers lifetime in 1.39 InGaA5P. The crosses are the experimental inverse lifetimes. The dashed line is the calculated inverse radiative lifetime. The open circles are obtained by substracting the dashed line to the crosses and represent the non radiative part of the recombination. The dashed dotted line is a Can2 curve with Ca=2.6 10—29cm6s—1. The full line is the sum of the dashed and the dashed dotted line. 6 (Ca=2•7 1029cm6s~) and is lower than previous recent theoretical calculations measurements and calculations. Furthermore it shows that Auger coefficient does not increase with temperature as it was thought peviously. Anyhow, using the value of the Auger coefficient we have measured and the fact it is constant around room temperature, we can calculate the To value for 1.3p InGaA5P lasers taking into account a recycling of the photons of 1.5 in the active layer. We find T 0=121K (a value larger than the one observed on lasers:5O—90K) which shows that Auger recombination is not sufficient to explain these small T0 values. REFERENCES 1) Y. Horikoshi in : 379—411 InGaAsP alloy semiconductors, ed. T.P. Pearsall (J. 1982)H.d. pp. Eichler, d.P. Heritage, R.J. Nelson and N.K. Dutta, Appl. 2) B.Wiley, Semmage, Phys. Lett. 42, 259 (1983) 3) E. Wintner and E.P. Ippen, Appl. Phys. Lett. 44, 999 (1984) 4) H.L. Casey and M.B. Panish, Heterostructure lasers, Academic press, New York 1978, p.129 5) T.P. Pearsall in : InGaA5P alloy semiconductors, ed. T.P. Pearsall (J. Wiley, 1982) pp. 295—312 6) M. Takeshima, Phys rev.B, 29, 1993 (1984)