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EFFECT OF SELECTIVE DOPING ON THE LUMINESCENCE RESPONSE OF A HEAVILY
Si-DOPED GaAs/AlGaAs QUANTUM WELL
N. Kamata, H. Tsuchiya, K. Kobayashi, T. Suzuki
To cite this version:
N. Kamata, H. Tsuchiya, K. Kobayashi, T. Suzuki. EFFECT OF SELECTIVE DOPING ON THE LUMINESCENCE RESPONSE OF A HEAVILY Si-DOPED GaAs/AlGaAs QUANTUM WELL.
Journal de Physique Colloques, 1987, 48 (C5), pp.C5-399-C5-402. �10.1051/jphyscol:1987585�. �jpa-
00226789�
C o l l o q u e C5, s u p p l 6 m e n t a u n " l 1 , Tome 48, novembre 1987
EFFECT OF SELECTIVE DOPING ON THE LUMINESCENCE RESPONSE OF A HEAVILY Si-DOPED GaAs/AlGaAs QUANTUM WELL
N. KAMATA, H. TSUCHIYA, K. KOBAYASHI* and T. SUZUKI*
ATR Optical and Radio Communications Research Zaboratories, Twin 21 MID Tower, 2-1-61 Shiromi, Higashi-ku, Osaka 540, Japan
'science and Technical Research Laboratories, NHK 1-10-11 Kinuta, Setagaya-ku, Tokyo 157, Japan
Les c a r a c t 6 r i s t i q u e s d e 1 ' &mission spontan6e dans une couche a c t i v e fortement do&e ont &t& grandement am6lior8es en u t i l i s a n t une s t r u c t u r e d e dopage s 8 l e c t i o n n b e . L a s d p a r a t i o n s p a t i a l e e n t r e les impuretgs e t l e s recombinaisons des p o r t e u r s m a j o r i t a i r e s a v e c les minoritaires a glimini! l a formation de centres de recombinaisons non- r a d i a t i v e s dans l e p i t s de p t e n t i e l .
Spontaneous emission c h a r a c t e r i s t i c s i n a h e a v i l y doped a c t i v e l a y e r have s u c c e s s f u l l y been improved by u s i n g a s e l e c t i v e doping structure. S p a t i a l separation of impurities frcm recombining m j o r i t y and minority c a r r i e r s has eliminated the formation of impurity-related nonradiative centers frcm the w e l l layer.
1. Introduction
Ificrease i n t h e doping density of a semiconductor a c t i v e layer broadens t h e mdulation badwidth of spontaneous l i g h t emission1). When S i is doped i n GAS;
however, emission e f f i c i e n c y d e c r e a s e s r a p i d l y above a c a r r i e r d e n s i t y of 3x1
o1
2). Since t h e c o n t r i b u t i o n of c a r r i e r compensation and Auger reccanbination3) is not y e t daminant a t t h i s region, the main cause i s thought t o be a kind of n o n r a d i a t i v e c e n t e r generated by t h e excess i n c o r p o r a t i o n of S i atoms in the crystal. A s it is electrons and b l e s t h a t mst be present to f u l f i l l t h e r a d i a t i v e recombinaticn, impurity a t m s must be s p a t i a l l y separated f r m the recombination region, provided t h a t s u f f i c i e n t m j o r i t y c a r r i e r s a r e s u p p l i d . By photoluminescence pulse response measurements, an a p p l i c a t i m of s e l e c t i v e doping4) has been shown t o be e f f e c t i v e a t t h e heavy doping region.2. Experimental
Ten ~ e r i o d s of a quantum well (QW) structure with a unit cjC 100i GaAs well and 500i A10-22Ga0.78As b a r r i e r were grown on a (100) s e m i - i n s u l a t i n g GaAs s u b s t r a t e by KBE technique5). Growth temperature was s e t a t 600'~ with a f l u x
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987585
C5-400 JOURNAL DE PHYSIQUE
ratio FV/~III=l -4 and a growth rate of 1.4p/h. Two different doping profiles were adopted for this experiment. Selectively doped(SD) sample(Fig.1 (a)) has Si impurities(density of nb) only in the center part of the barrier layer. In addition, uniformly doped(UD) sample(Fig.1 (b)) with a Si doped well-layer is provided for the sake of comparison. The well-layer Si density rt, of the UD sample is 28%(the gr&h rate ratio) higher than nb. Spacer thicknesses in both schemes are 120W at the substrate-side interface and 40A at the surface-side.
The sheet electron density per unit QW Ns, which includes electrons both in a well and in a barrier, is determined by a Hall measurement. The formation of 2- dimensional electrons in a SD sample was confirmed by the mobility enhancement at 7 7 ~ ~ ) .
Figure 2 represents the normalized photoluminescence spectra of b t h SD and UD samples at room temperature under 514.5nm Ar laser excitation. Si in- corporation density in the barrier nb(cm-3) is varied as follows: (a) 3.3x1017
(b) 1.6~10~ (c) 7.3~10' and (d) 1.7~10~
'.
The lineshape of the QW emission is extracted frcm the total emission spectra which includes below-gap canpnents from the Si- doped layer. Photoluminescence pulse response was measured by mode-locked pulse excitation with the half-width of less than 150ps.Luminescence output was observed by an avalanche photodiode. Figure 3 shows typical SD sample photoluminescence response. As can be seen in the figure, response time decreases as Si density increases. The situation was also the same for UD samples. Recombination lifetime is obtained by the response waveform taking detector bandwidth into account. In Fig.4, the CYl emission intensity P, the recombination lifetimexand the sheet electron density per unit QW Ns are plotted as a function of the Si incorporation (reciprocal of the Si cell temperature TSi). The intensity of SD samples maintains a relatively high efficiency when compared with the UD samples, which is clearly seen at Ns=l .6x101 3cm-2. Observed recombination lifetime of SD sample is 0.611s at
~s=1.6x10~ 3un-2, which corresponds to 270MHz modulation bandwidth without any efficiency decrease.
3.Discussion
Effect of selective doping is considered briefly frcm these measurements.
In the region ~s<5x10' 2cm-2, no significant difference of Ns, P and is observed between SD and UD simples. The below-gap emission in this region originates from a recombination center in the barrier layer, since no difference
&tween SD and UD sample is observed. The lifetime shortening arises frcm the enhancement of the radiative recanbinaticn rate. This means that 2-dimensional electron density in a well nZD increases with the increase of Ns, though the ratio of n2D to electron density in a barrier decreases.
At the region 5x1 0~~crn-~<~s<1.6~10~ 3an-21 the situation of the SD samples is not changed. On the other hand, light output of the UD sample decreases rapidly, though Ns increases monotonically with the increase of Si incorporation. The dominant nonradiative process in the UD sample is related to a high density incorporation of Si atcms in the well layer, since the SD sample without a sufficient spacer thickness also shows the same output reduction. The higher mission efficiency of SD samples is therefore attributed to the spatial separation of impurity atom from recombining majority and minority carriers in the well layer. This separation eliminates the formation of band tail and the Si-related nonradiative centers from the well layer where carrier recombination
samples reaches its limit6) and further decrease in is due to the nonradiative recombination rate. The spectral change observed in Fig.4 suggests a developnent of recombination centers at the hetero-interface.
The scheme of selective doping can be also applied to P-type doping7) and such other heterostructure systems as InGaAs/InAlAs, InGaAsP/InP etc.
4. Conclusion
Photoluminescence output efficiency and pllse response £ran a Ga~s/~lGaAs multiple QW show that improved emission characteristics are obtained by using a selective doping structure at Ns around 1.6~1
an-^.
This structure shortens the recombination lifetime without any efficiency reduction and is pranking for high speed LEDs and laser diodes. Spatial separation of impurities from the light generating region where recombining majority and minority carriers are accumulated is essential in this structure.Acknwledgements
The authors wish to express their sincere gratitude to Dr.Hisashi Katahama ad Mr.Yukio Shakuda for their experimental help and stimulating discussions.
References
1 )K.Ikeda, S.Horiuchi ,T.Tanaka and w.Susaki: IEEE Trans. Electron Devices ED-24 (1977) 1001.
2)J.H.Neave1P.J.Dobs0n1 J.J.Harris,P.Dawson and B.A.Joyce:Appl. Phys. A32 (1 983 )
195.
3)N.K.Dutta and R.J.Ne1son:Appl.Phys.Lett. 38 (1981 ) 407.
4)RDingle,KL.Stormer,RC.Gossard and W.Wiemann:Appl.Phys.Lett. 46 (1 985) 973.
5)N.KamatarK.Kobayashi and T.Suzuki:Proc. Int. Symp. GaAs and Related Cunpounds, Karuizawa, 1985 (Inst. Phys. Conf. Ser. No.79, 1986) p.691.
6)W.P.Dumke:Phys.Rev. 132 (1 963) 1998.
7 )K.Uomi ,T.Ohtoshi and N.Chinone: Proc. IEEE 1nt.Semiconductor Laser Conf .(I 986) M-6.
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Fig.1 Schematic energy band diagram of ( a ) S D and ( b ) UD samples.
1.0 -
R.T.
0.0
---I--- I700 800 900 1000 1100 WAVELENGTH
A (nm
Fig.2 Photoluminescence swectra a t ram . - - - tem~erature S i incorporation density is v a r i e d f r m ( a ) 3 . 3 ~ 1 0 ~ ~ c m - ~ t o ( d ) 1 .7x1 ~ ' ~ c m -
8 .
~ ~ ( c m - ~ ) 1.3~10'~
0.5nsldiv.
1.6x1d3 0.5nsldiv.
-
CP
W
2.5~1 0l3
1F
I- z
W W
0.2nsIdi~
LL-
-1I :
0.1
I
0
8.0 7.5 7.0
Fig.3 Time response of SD sample photo- luminescence.
1 0 ~ 1 ~ ~ ~ (K-')
Fig.4 Sheet c a r r i e r density per QW N integrated i n t e n s i t y of the quantum we?i e m i s s i o n P and the recombination l i f e - time -C as a function of S i i n c o w r a t i o n ( r e c i p r o c a l of S i c e l l temperature).
