Stress distribution and dislocation dynamics in GaAs grown on Si by metalorganic chemical vapor deposition

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CRYSTAL GROWTH

ELSEVIER

Journal of Crystal Growth 145 (1994) 321—325

Stress distribution and dislocation dynamics in GaAs grown on Si by metalorganic chemical vapor deposition Yoshiki Naoi

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Satoshi Kurai, Shiro Sakai, Tao Yang

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Yoshihiro Shintani

Department of Electrical and Electronic Engineering, The University of Tokushima, Minami-Josanjima 2-1, Tokushima 770, Japan

Abstract We have investigated, by photoluminescence measurement, the microscopic stress distribution near the dislocation in GaAs grown on Si substrate and in planar homoepitaxial GaAs which was grown by metalorganic chemical vapor deposition (MOCVD). It was found that a compressive stress due to lattice deformation existed near the dislocation. Dislocation dynamics were observed by photoluminescence image while applying the external stress by a fine needle. Density and location of the dislocation could be artificially operated by some extent.

1. Introduction GaAs grown on Si substrate is very promising in optoelectronic integrated circuits which are useful, for example, in optical interconnection, However, a GaAs light emitter fabricated on Si substrate degrades rapidly due to the large residual stress and the high density of dislocations. We have proposed the UCGAS (undercut GaAs on Si) structure, in which a part of the grown layer is separated from the Si substrate, to overcome the problems [1]. The UCGAS structure has attained 2, a dislocation a stress below 2 x 108 dyn/cm density of the order of iO~cm2 and an operation life time of light emitting diode of more than 3000 h [2]. In addition, we have found, by high

*

Corresponding author.

1

On leave from Harbin Institute of Technology, Harbin,

People’s Republic of China,

magnification photoluminescence

image (PU),

that some of the dark spots (DSs) in PU, which had originated from the dislocation and nonradiative recombination center, move after laser beam irradiation [3]. The number and the speed of the moving DSs are larger in those samples that contain higher DS density and residual stress. The driving forces of these phenomena are considered to be the stress and the laser beam energy which is transferred to the crystal lattice through non-radiative recombination. However, microscopic stress near the dislocation has not been measured so far. It is important to make clear this mechanism to investigate laser degradation. It may also be possible to control the location of the DS by applying external force or energy. This DS manipulation enables the fabrication of devices in the dislocation-free regions, since DS density of iO~cm2 corresponds to one DS in every 30 ~m which is larger than the practical devices. In this paper, we discuss the

0022-0248/94/$07.OO ~ 1994 Elsevier Science B.V. All rights reserved SSDI 0022-0248(94)00269-R

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Y Naoi et a!. /Journal of Crystal Growth 145 (1994) 321-325

stress and the dislocation dynamics in GaAs ~

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~ /1’ The samples used in this experiment were grown by low pressure MOCVD. The sample structures are shown in Fig. 1. In sample A, GaAs layers were grown on 4° off Si (100) substrate. The fabrication procedure of the UCGAS structure was described elsewhere [1]. Sample B was fabricated on GaAs substrate. The top layer of both samples was doped with Si to obtain clear photoluminescence image (PU) at room temperature. The dislocation densities samples A and 2 in and less than iO~ B are of the order of 108 crn cm2, respectively. 2.2. Photoluminescence measurement Two kinds of PL measurement were performed at room temperature. One is the PU observation, the other is the measurement of PL spectra in a small region. The measurement systern is shown in Fig. 2. PU was observed by the system consisting of high magnification optical microscope (x 550) and infrared camera. The

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samples were placed under the optical microscope (Olympus BHM-313MU), and the 488 nm line of an ion laser focused to elliptical shape of argon 80 x 150 .tm2 was on the sample surface. The excitation power density was about 0.4 to 2 kW/cm2. PU was observed by infrared camera (Hamamatsu C2741) attached to the microscope through a visible light cut optical filter. In the PL spectrum measurement, PL light was guided to the entrance of the optical fiber through the half-mirror in the microscope, and was analyzed by a spectrometer (Jobin-Yvon HR-640). By scanning the optical fiber location at the exit of the microscope, it was possible to obtain the mapping of the PL spectra as a function of the location on

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Y. Naoi et al. /Journal of Crystal Growth 145 (1994) 321—325

the sample surface. The spatial resolution in this measurement was evaluated to be 1.4 jim. 3. Results and discussions 3.1. Stress distribution in the DS Figs. 3a, 3b and 3c show the PLI on the center of the UCGAS part in Fig. la, the contour map

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of the PU peak wavelength as a function of the location on the sample surface, and the PU peak intensity against the PL peak wavelength measured in an area of 2.5 x 2.5 ~sm2on GaAs grown on Si substrate, respectively. The PU spectra in the area of 2.5 x 2.5 p.m2 on the sample surface are measured with 0.5 p.m steps (total number of measurement is 36). Since the DS density is of the order of 108 cm 2, which corresponds to one DS in every 1 ~sm, 6 or 7 DSs should exist in the measurement area of 2.5 X 2.5 p.m2. The DSs in this sample are too high to find a clear relation between the dark spot in the PUI and the PU peak wavelength. However, Fig. 3c shows a strong positive relation between PU peak wavelength and intensity, with the correlation coefficient of 0.47 meaning that the PU peak wavelength is shorter in the DS. This indicates that the stress exists in the dislocation, because a DS in which PU intensity is low has relatively shorter PU peak wavelength and the PU peak wavelength measured in the large area is 858 nm. homoepitaxial GaAs as those for GaAs grown on

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Si Fig. substrate. 4 shows Thethe PUsame spectra results wereonmeasured the planar in shows that DSs exist locally on the sample surface, and the DS density is less than iO~cm2. the area of 10 x 10 p.m2 with 2 p.m steps. Fig. 4a By comparing Figs. 4a and 4b, the one-to-one correspondence between the DS and the area of short PL peak wavelength is clear. The PL peak wavelength and intensity have a positive relation with the correlation coefficient of 0.63. Since the PL peak wavelength of 868.8 nm measured in the wide area, which is the PU peak wavelength for stress-free GaAs, is longer than that in the DS,

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compressive stress of approximately 3 x 108 dyn/cm2 exists in the dislocation, as the wavelength shift is about 2.0 nm [4]. The PU wavelength of this compared with those on measurement the UCGAS, cannot becausebethe excited

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PL Peak Wavelength (nm] Fig. 3. Results in GaAs on Si: (a) PLI; (b) contour map of the PL peak wavelength; (c) PL peak intensity versus PL peak wavelength. Marker in (a) represents 20 ~m.

3.2. DS dynamics Fig. 5 shows typical PUs when the external stress is applied by pushing the surface of planar

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homoepitaxial GaAs by a fine needle (tip curvature is approximately 5 p.m) and moving the needle from left to right in Fig. 5. The stress applied to the surface is evaluated to be of 2, which is the aporder of 2.0the ±1.5 X 108 dyn/cm proximately same as the stress existing in the

DS. The DS near the tip moves by applying the external stress, and the PU intensity is increased probably due to the decrease in the number of small Therefore, densityoperated and location of the defects. dislocation can be the artificially to a certain extent. This is the first demonstration of DS manipulation by external stress, and suggests the possibility of making devices in the dislocation-free regions.

4. Conclusions

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We have measured the mapping of the PU peak wavelength and PUI in a small area on GaAs grown on Si substrate and on planar homoepitaxial GaAs. We found the relation between PU peak wavelength and intensity, and showed that compressive stress existed in the dislocation due to the lattice deformation. We demonstrated, for the first time, that the density and the location of the dislocation could be artificially operated to some extent by pushing the sample surface by a fine needle. This suggests the possibility of manipulating DS by a needle Acknowledgments

Fig. 5. PU from homoepitaxial planar GaAs: (a) before, (b) during, and (c) after applying the external stress. The DS marked by an arrow is moving and PL Intensity is increased after applying the external stress by a fine needle. Marker represents 10 ~tm.

We would like to thank Dr. N. Wada of Matsushita Kotobuki Electronics Industries, Ltd., for .

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his advice in growing samples and in the measurement. This research was supported in part by

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Y. Naoi et a!. /Journal of Crystal Growth 145

(1994)

321—325

325

a Grand-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture.

[2] N. Wada, S. Sakai, S. Yoshimi, Y. Shintani and M. Fukui, Jap. J. AppI. Phys. 33 (1994) 1268. [3] N. Wada, S. Sakai and M. Fukui, Jap. J. AppI. Phys. 33 (1994) 864.

References

[4] S. Zemon, S.K. Shastry, P. Norris, C. Jagannath and G. Lanbert, Solid State Commun. 58 (1986) 457.

[1] N. Wada, S. Sakai and M. Fukui, Jap. J. Appl. Phys. 33 (1994) 976.

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