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Shallow diffusion of zinc into GaAs for optical waveguide modulators
Thin Solid Films, 83 (1981) 289-293 ELECTRONICS AND OPTICS
289
SHALLOW DIFFUSION OF ZINC INTO GaAs FOR OPTICAL WAVEGUIDE MODULATORS* K. TADA, T. SUZUKI AND K. YAMANEt
Department of Electronic Engineering, the University of Tokyo, Bunkyo-ku, Tokyo, 113 (Japan) (Received April 6, 1981 ; accepted April 8, 1981)
We developed a diffusion technique for the fabrication of a coupled-waveguide optical modulator with a p-n junction in a strip-loaded channel-waveguide configuration, zinc was diffused into n-type GaAs at 580 °C for 2 h in a closed tube. The diffused p+ layer was as thin as 1.3 lam, and the stepwise diffusion profile was explained using the theory of substitutional-interstitial diffusion. The modulator was formed by chemical etching on an n/n ÷-GaAs wafer prepared by vapour phase epitaxy with subsequent diffusion of the p+ surface layer.
l. INTRODUCTION
Among various optical waveguide modulators the coupled-waveguide modulator (the electrically switched optical directional coupler) is one of the most promising devices, since it can perform various functions including modulation, switching, variable directional coupling and filtering. The principle of this device is the evanescent coupling of optical waves between two parallel waveguides which are placed very close to each other. The coupling efficiency of optical power from one waveguide to the other is modulated by perturbing the synchronism in the phase velocities of two optical guided waves 1-4. This device was realized for the first time in 1974 as a GaAs device with a p-n junction in a multilayered planar waveguide configuration 5. To improve this, another device with a p-n junction in a strip-loaded channel-waveguide configuration was proposed 6 and has been analysed in detail ~. The device structure is shown schematically in Fig. 1. It is expected that this device will have a very low modulating power per bandwidth P/Afand a very wide bandwidth Af. For example, P/Afand Afhave been calculated to be 22 laW M H z - 1 and 10 GHz respectively in a GaAs/Alo.~4Gao.s6As double-heterostructured device of length 3.5 mm, strip width 5 I~m and strip spacing 2.5 ~tm 7. Recently, we succeeded in fabricating the first example of this type of device. The details will be published separately. Briefly, the * Paper presented at the International. Conference on Metallurgical Coatings, San Francisco, CA, U.S.A., April 6-10, 1981. t Present address: Fujitsu Ltd., Nakahara-ku, Kawasaki 211, Japan. 0040-6090/81/0000-0000/:$02.50
© Elsevier Sequoia/Printed in The Netherlands
290
K. TADA, T. SUZUKI, K. YAMANE
ELECTRODE~ (;01)
~ ELECTRODE (iio)
Fig. 1. Schematic diagram of a coupled-waveguide optical modulator with a p--n junction in a striploaded channel-waveguide configuration.
strips were formed by chemically etching a p+ layer in p+-Alo.o4Gao.96As/nGaAs/n+-Alo.o4Gao.96As double-heterostructured layers grown on a GaAs substrate by liquid phase epitaxy. Because of the very long but thin dimensions of this device, however, it was not easy to fabricate it on a GaAs/AlxGa 1_xAs wafer by liquid phase epitaxy which tends to produce a rough surface morphology. One way to solve this problem is to use wafers with smoother surfaces grown by vapour phase epitaxy (VPE) or molecular beam epitaxy. Firstly, using such wafers and replacing the p-n junction with a Schottky contact, we can fabricate without much difficulty a coupled-waveguide modulator with a Schottky contact in a ribwaveguide configuration8-~ 1. The second approach is to form a p-n junction in the top n layer of an n/n ÷-GaAs wafer with a smooth surface grown by VPE. We investigated the thermal diffusion of zinc into GaAs at temperatures below 600 °C and obtained a thin p+ layer about 1 pm thick which is suitable for the strip layer in the coupled-waveguide modulator. The measured diffusion profile of zinc is explained in terms of the theory of substitutional-interstitial diffusion. We fabricated the modulators on such VPE wafers with a diffused p+-n junction and a smooth fiat surface. In the following sections the experifnental method and results in this new approach are reported in detail. 2. SHALLOW DIFFUSION OF ZINC INTO GaAs The diffusion of zinc into GaAs has been studied extensively at high temperatures (around 1000 °C), and anomalous diffusion profiles in these thick (several tens of microns) diffused layers have been explained in terms of the theory of substitutional-interstitial diffusion12-17. However, no published data were available to us on the diffusion of zinc into GaAs at temperatures around 600 °C. Therefore, after several attempts we carried out the following experiments and obtained a thin diffused layer which was suitable as the strip layer of the modulator. The diffusion was undertaken in a closed tube. GaAs wafers with n-type conduction and the diffusion source (0.2 g Zn plus 0.15 g ZnAs2) were placed at separate positions inside an evacuated and sealed quartz ampoule of diameter 20 mm and length 15 cm, as illustrated in Fig. 2. The ampoule was slowly and carefully pulled into and out of a three-zone resistance-heated diffusion furnace. It was
GaAs FOR OPTICAL WAVEGUIDE MODULATORS
DIFFUSION OF Z n INTO
291
Sealing-Plug Zn, ZnAs2
GaAs Wafer
GaAB
Fig. 2. Quartz ampoule ready for the diffusion experiment.
observed that the zinc source sputtered badly at its melting point (420 °C) if the rise in temperature was too sudden. Care was also taken that the temperature of the GaAs wafers was always higher than that of the source. Typically, the wafers and the source were held at 580 °C and 564 °C respectively for 2 h. The p÷-n junction depth was measured by lapping the surface of the sample with a spherical drill and then staining the sample with 30~o aqueous nitric acid. An example is shown in Fig. 3, for which the measured depths are 1.13 ~la, 1.10 ~tm and 0.98 ~m for wafers with donor concentration of 5 x 1014 cm -a, 1 x 1016 cm -3 and 1 × 1018 cm-3 respectively. Near the surface the concentration of the diffused zinc was evaluated by measuring the Hall coefficient and then step etching the thin top layer of the sample, this sequence being repeated several times. An example of the diffusion profile thus obtained is plotted in Fig. 3 (open circles). The surface concentration Cs, r (solubility) of zinc was measured as 4.5 x 1019 cm -3 in this sample. The zinc concentration C decreased gradually near the surface and then dropped sharply near the p+-n junction. The junction capacitance measured as a function of the reverse voltage also indicated that the junction was almost stepwise. The diffusion of zinc into GaAs can be explained using the theory of substitutional-interstitial diffusion12-17. The zinc atom joins the lattice at the surface, becomes interstitial and diffuses through the lattice very rapidly. It
1020 ~--~ ° ~ o
~ - ~ - ~ o ~.~....~
1019
10IB
1017
IOz6
lOIs
o
I
I
I
I
I
I
0,2
0.4
0,6
0,8
1,0
1,2
>
DEPTHX(:m)
Fig. 3. Zinc concentration profile after diffusion at 580 °C for 2 h.
292
K. TADA, T. SUZUKI, K. YAMANE
eventually combines with a gallium vacancy and becomes substitutional again. The following reaction is considered to occur 16,17. Zni + -[- VGa ~ Z n s - + 2 h + (1) If the vacancy concentration drops below its equilibrium value the diffusion profile can be quite complex, as is usually observed in much thicker diffused layers. In our experiment, however, the vacancy equilibrium is considered to be maintained in the shallow diffused layer owing to the vacancy diffusion from the surface. By assuming further that the interstitial zinc has a much greater diffusion coefficient but a much lower concentration than the substitutional zinc, we can derive the diffusion equation
t~t - ~3x Ds"r
~-x
(2)
This shows that the effective diffusion coefficient is proportional to the square of the zinc concentration. The full curve in Fig. 3 is the theoretical profile calculated numerically from eqn. (2) and is in fair agreement with the experimental results. This theory also indicates that C / C s , , sharply approaches zero at a diffusion depth given by x d ~ 0.546(4Ds,~T) U2 where 7- is the diffusion time 12. Thus the effective diffusion coefficient Ds,~ at the surface is calculated to be 1.5 x 10-12 cm 2 s- 1 in this particular sample. After several similar experiments we concluded that at 580°C Cs, r = (4.5+ 1.5)x 1019 cm -3, Dsu, = (1.9 + 0.4) x 10- t2 cm 2 s-1, and the diffusion depth of about 1.3 pm (1.1-1.4 ~tm) is obtained reproducibly for a diffusion time of 2 h. Diodes were fabricated on these zinc-diffused GaAs wafers. The ohmic contact for the n-type substrate was prepared from Au-12wt.9/oGe-5wt.9/oNi which had been alloyed at 420 °C, and that for the p ÷-type diffused layer was simply evaporated Au10wt.~oZn. The area of the latter electrode was typically 7.5 × 10-a cm 2 and the donor concentration in the substrate was 1014-1016 cm-a. The breakdown voltage of these diodes was 8-11 V, and the diode factor ," in the forward direction was about 2. 3. FABRICATION OF MODULATORS The wafer used for the actual modulators had an n-GaAs layer 5 lam thick with a donor concentration of 2 x 1013 cm-3. It was grown by VPE directly on the n +GaAs substrate which had a donor concentration of 2 x 10 is c m - 3. By applying the equivalent refractive index method 7, a modulator With the structure shown in Fig. 1 fitted to the above wafer was designed with the following parameters: strip width, 4 Ism; strip spacing, 7.5 pm; strip height, 0.5 ~ n ; guide layer thickness, 2.5 lxm; device length, 6.7 mm; electrode capacitance, 1.2 pF; bandwidth, 5.2 G H z ; switching voltage, 27 V; modulating power per bandwidth for 1009/o modulation, 350 ~tW M H z - 1. Here, it was assumed that the TE-like fundamental mode at a wavelength of 1.06 lam was employed and that only one electrode was actuated. In accordance with this design, the thickness of the n-GaAs layer was first reduced to 3.9 lam by chemical etching in H 3 P O 4 - H 2 0 2 - H 2 0 with a volume ratio
DIFFUSION OF Zn INTO
GaAs FOR OPTICAL WAVEGUIDE MODULATORS
293
of 1:1: 8 at 25 °C. Then the wafer was subjected to the zinc diffusion as described in the previous section. After an ohmic contact to the substrate had been formed, the diffused p+ layer was further etched to a thickness of 0.5 ~n. A thin gold film was evaporated as an ohmic contact, and then the positive photoresist AZ1350B was spin coated, exposed and developed. After the electrode pattern had been formed by chemical etching of the gold film in I2-KI-H20 with a weight ratio of 1:6: 80, the strip-loaded waveguides were formed by chemically etching a p+ layer in the HaPO4-H202-H20 solution mentioned above. Radiation from an Nd 3 +:YAG laser at 1.06 pm was focused onto the cleaved input face of the fabricated samples. They operated as optical directional couplers. However, the breakdown voltage in these modulators was found to be much lower than that in the diodes described in Section 2. A modulation experiment could not be carried out. Improvement in the breakdown characteristics is urgently needed for the future development of this device. 4. CONCLUSIONS We have described a technique for the thermal diffusion of zinc into GaAs which was developed to produce a very thin p+ layer on a smooth surface of an nGaAs wafer. The diffusion was carried out by a closed-tube method at 580 °C for 2 h using a source of zinc plus ZnAs2. The thickness of the diffused layer was approximately 1.3 ~tm and the surface concentration of zinc was about 4.5 x 1019 cm- 3. The diffusion profiles were found to be stepwise, and this was explained using the theory of substitutional-interstitial diffusion. We also developed fabrication techniques for a coupled-waveguide optical modulator with a p-n junction in a strip-loaded channel-waveguide configuration, using an n/n ÷-GaAs wafer prepared by VPE with a thin diffused p+ surface layer. REFERENCES
1 E.A.J. Marcafili, BelISyst. Tech. J.,48(1969)2071. S. Kurazono, K. Iwasaki and N. Kumagai, Trans. Inst. Electron. Commun. Eng. Jpn., Sect. C, 55
2
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
(1972) 61. H.F. Taylor, J. Appl. Phys., 44 (1973) 3257. H. Kogelnik and R. V. Schmidt, IEEEJ. Quantum Electron., 12 (1976) 396. K. Tada and K. Hirose, Appl. Phys. Lett., 25 (1974) 561. K. Hirose, K. Tada and H. Yanagawa, Jpn. J. Appl. Phys., 16-S1 (1977) 311. K. Tada, H. Yanagawa and K. Hirose, Trans. Inst. Electron. Commun. Eng. Jpn., Sect. E, 61 (1978) 1. K.,Tada and H. Yanagawa , J. Appl. Phys., 49 (1978) 5404. K. Tada, H. Yanagawa and Y. Matsunaga, Jpn. J. Appl. Phys., 18-S1 (1979) 393. H. Kawaguchi, Jpn. J. Appl. Phys., 18-S1 (1979) 385. A. Carenco, L. Menigaux, F. Alexandre, M. Abdalla and A. Brenae, Appl. Phys. Lett., 34 (1979) 755. L.R. Weisberg and J. Blanc, Phys. Rev., 131 (1963) 1548.
L. L. Chang and G. L. Pearson, J. AppI. Phys., 35 (1964)1960. K.K. Shih, J. W. Allen and G. L. Pearson, J. Phys. Chem. Solids, 29 (1968) 379. B. Tuck, J. Phys. Chem. Solids, 30 (1969) 253. M . A . H . Kadhim and B. Tuck, J. Mater. Sci., 7 (1972) 68. B. Tuck and M. A. H. Kadhim, J. Mater. Sci., 7 (1972) 581.
289
SHALLOW DIFFUSION OF ZINC INTO GaAs FOR OPTICAL WAVEGUIDE MODULATORS* K. TADA, T. SUZUKI AND K. YAMANEt
Department of Electronic Engineering, the University of Tokyo, Bunkyo-ku, Tokyo, 113 (Japan) (Received April 6, 1981 ; accepted April 8, 1981)
We developed a diffusion technique for the fabrication of a coupled-waveguide optical modulator with a p-n junction in a strip-loaded channel-waveguide configuration, zinc was diffused into n-type GaAs at 580 °C for 2 h in a closed tube. The diffused p+ layer was as thin as 1.3 lam, and the stepwise diffusion profile was explained using the theory of substitutional-interstitial diffusion. The modulator was formed by chemical etching on an n/n ÷-GaAs wafer prepared by vapour phase epitaxy with subsequent diffusion of the p+ surface layer.
l. INTRODUCTION
Among various optical waveguide modulators the coupled-waveguide modulator (the electrically switched optical directional coupler) is one of the most promising devices, since it can perform various functions including modulation, switching, variable directional coupling and filtering. The principle of this device is the evanescent coupling of optical waves between two parallel waveguides which are placed very close to each other. The coupling efficiency of optical power from one waveguide to the other is modulated by perturbing the synchronism in the phase velocities of two optical guided waves 1-4. This device was realized for the first time in 1974 as a GaAs device with a p-n junction in a multilayered planar waveguide configuration 5. To improve this, another device with a p-n junction in a strip-loaded channel-waveguide configuration was proposed 6 and has been analysed in detail ~. The device structure is shown schematically in Fig. 1. It is expected that this device will have a very low modulating power per bandwidth P/Afand a very wide bandwidth Af. For example, P/Afand Afhave been calculated to be 22 laW M H z - 1 and 10 GHz respectively in a GaAs/Alo.~4Gao.s6As double-heterostructured device of length 3.5 mm, strip width 5 I~m and strip spacing 2.5 ~tm 7. Recently, we succeeded in fabricating the first example of this type of device. The details will be published separately. Briefly, the * Paper presented at the International. Conference on Metallurgical Coatings, San Francisco, CA, U.S.A., April 6-10, 1981. t Present address: Fujitsu Ltd., Nakahara-ku, Kawasaki 211, Japan. 0040-6090/81/0000-0000/:$02.50
© Elsevier Sequoia/Printed in The Netherlands
290
K. TADA, T. SUZUKI, K. YAMANE
ELECTRODE~ (;01)
~ ELECTRODE (iio)
Fig. 1. Schematic diagram of a coupled-waveguide optical modulator with a p--n junction in a striploaded channel-waveguide configuration.
strips were formed by chemically etching a p+ layer in p+-Alo.o4Gao.96As/nGaAs/n+-Alo.o4Gao.96As double-heterostructured layers grown on a GaAs substrate by liquid phase epitaxy. Because of the very long but thin dimensions of this device, however, it was not easy to fabricate it on a GaAs/AlxGa 1_xAs wafer by liquid phase epitaxy which tends to produce a rough surface morphology. One way to solve this problem is to use wafers with smoother surfaces grown by vapour phase epitaxy (VPE) or molecular beam epitaxy. Firstly, using such wafers and replacing the p-n junction with a Schottky contact, we can fabricate without much difficulty a coupled-waveguide modulator with a Schottky contact in a ribwaveguide configuration8-~ 1. The second approach is to form a p-n junction in the top n layer of an n/n ÷-GaAs wafer with a smooth surface grown by VPE. We investigated the thermal diffusion of zinc into GaAs at temperatures below 600 °C and obtained a thin p+ layer about 1 pm thick which is suitable for the strip layer in the coupled-waveguide modulator. The measured diffusion profile of zinc is explained in terms of the theory of substitutional-interstitial diffusion. We fabricated the modulators on such VPE wafers with a diffused p+-n junction and a smooth fiat surface. In the following sections the experifnental method and results in this new approach are reported in detail. 2. SHALLOW DIFFUSION OF ZINC INTO GaAs The diffusion of zinc into GaAs has been studied extensively at high temperatures (around 1000 °C), and anomalous diffusion profiles in these thick (several tens of microns) diffused layers have been explained in terms of the theory of substitutional-interstitial diffusion12-17. However, no published data were available to us on the diffusion of zinc into GaAs at temperatures around 600 °C. Therefore, after several attempts we carried out the following experiments and obtained a thin diffused layer which was suitable as the strip layer of the modulator. The diffusion was undertaken in a closed tube. GaAs wafers with n-type conduction and the diffusion source (0.2 g Zn plus 0.15 g ZnAs2) were placed at separate positions inside an evacuated and sealed quartz ampoule of diameter 20 mm and length 15 cm, as illustrated in Fig. 2. The ampoule was slowly and carefully pulled into and out of a three-zone resistance-heated diffusion furnace. It was
GaAs FOR OPTICAL WAVEGUIDE MODULATORS
DIFFUSION OF Z n INTO
291
Sealing-Plug Zn, ZnAs2
GaAs Wafer
GaAB
Fig. 2. Quartz ampoule ready for the diffusion experiment.
observed that the zinc source sputtered badly at its melting point (420 °C) if the rise in temperature was too sudden. Care was also taken that the temperature of the GaAs wafers was always higher than that of the source. Typically, the wafers and the source were held at 580 °C and 564 °C respectively for 2 h. The p÷-n junction depth was measured by lapping the surface of the sample with a spherical drill and then staining the sample with 30~o aqueous nitric acid. An example is shown in Fig. 3, for which the measured depths are 1.13 ~la, 1.10 ~tm and 0.98 ~m for wafers with donor concentration of 5 x 1014 cm -a, 1 x 1016 cm -3 and 1 × 1018 cm-3 respectively. Near the surface the concentration of the diffused zinc was evaluated by measuring the Hall coefficient and then step etching the thin top layer of the sample, this sequence being repeated several times. An example of the diffusion profile thus obtained is plotted in Fig. 3 (open circles). The surface concentration Cs, r (solubility) of zinc was measured as 4.5 x 1019 cm -3 in this sample. The zinc concentration C decreased gradually near the surface and then dropped sharply near the p+-n junction. The junction capacitance measured as a function of the reverse voltage also indicated that the junction was almost stepwise. The diffusion of zinc into GaAs can be explained using the theory of substitutional-interstitial diffusion12-17. The zinc atom joins the lattice at the surface, becomes interstitial and diffuses through the lattice very rapidly. It
1020 ~--~ ° ~ o
~ - ~ - ~ o ~.~....~
1019
10IB
1017
IOz6
lOIs
o
I
I
I
I
I
I
0,2
0.4
0,6
0,8
1,0
1,2
>
DEPTHX(:m)
Fig. 3. Zinc concentration profile after diffusion at 580 °C for 2 h.
292
K. TADA, T. SUZUKI, K. YAMANE
eventually combines with a gallium vacancy and becomes substitutional again. The following reaction is considered to occur 16,17. Zni + -[- VGa ~ Z n s - + 2 h + (1) If the vacancy concentration drops below its equilibrium value the diffusion profile can be quite complex, as is usually observed in much thicker diffused layers. In our experiment, however, the vacancy equilibrium is considered to be maintained in the shallow diffused layer owing to the vacancy diffusion from the surface. By assuming further that the interstitial zinc has a much greater diffusion coefficient but a much lower concentration than the substitutional zinc, we can derive the diffusion equation
t~t - ~3x Ds"r
~-x
(2)
This shows that the effective diffusion coefficient is proportional to the square of the zinc concentration. The full curve in Fig. 3 is the theoretical profile calculated numerically from eqn. (2) and is in fair agreement with the experimental results. This theory also indicates that C / C s , , sharply approaches zero at a diffusion depth given by x d ~ 0.546(4Ds,~T) U2 where 7- is the diffusion time 12. Thus the effective diffusion coefficient Ds,~ at the surface is calculated to be 1.5 x 10-12 cm 2 s- 1 in this particular sample. After several similar experiments we concluded that at 580°C Cs, r = (4.5+ 1.5)x 1019 cm -3, Dsu, = (1.9 + 0.4) x 10- t2 cm 2 s-1, and the diffusion depth of about 1.3 pm (1.1-1.4 ~tm) is obtained reproducibly for a diffusion time of 2 h. Diodes were fabricated on these zinc-diffused GaAs wafers. The ohmic contact for the n-type substrate was prepared from Au-12wt.9/oGe-5wt.9/oNi which had been alloyed at 420 °C, and that for the p ÷-type diffused layer was simply evaporated Au10wt.~oZn. The area of the latter electrode was typically 7.5 × 10-a cm 2 and the donor concentration in the substrate was 1014-1016 cm-a. The breakdown voltage of these diodes was 8-11 V, and the diode factor ," in the forward direction was about 2. 3. FABRICATION OF MODULATORS The wafer used for the actual modulators had an n-GaAs layer 5 lam thick with a donor concentration of 2 x 1013 cm-3. It was grown by VPE directly on the n +GaAs substrate which had a donor concentration of 2 x 10 is c m - 3. By applying the equivalent refractive index method 7, a modulator With the structure shown in Fig. 1 fitted to the above wafer was designed with the following parameters: strip width, 4 Ism; strip spacing, 7.5 pm; strip height, 0.5 ~ n ; guide layer thickness, 2.5 lxm; device length, 6.7 mm; electrode capacitance, 1.2 pF; bandwidth, 5.2 G H z ; switching voltage, 27 V; modulating power per bandwidth for 1009/o modulation, 350 ~tW M H z - 1. Here, it was assumed that the TE-like fundamental mode at a wavelength of 1.06 lam was employed and that only one electrode was actuated. In accordance with this design, the thickness of the n-GaAs layer was first reduced to 3.9 lam by chemical etching in H 3 P O 4 - H 2 0 2 - H 2 0 with a volume ratio
DIFFUSION OF Zn INTO
GaAs FOR OPTICAL WAVEGUIDE MODULATORS
293
of 1:1: 8 at 25 °C. Then the wafer was subjected to the zinc diffusion as described in the previous section. After an ohmic contact to the substrate had been formed, the diffused p+ layer was further etched to a thickness of 0.5 ~n. A thin gold film was evaporated as an ohmic contact, and then the positive photoresist AZ1350B was spin coated, exposed and developed. After the electrode pattern had been formed by chemical etching of the gold film in I2-KI-H20 with a weight ratio of 1:6: 80, the strip-loaded waveguides were formed by chemically etching a p+ layer in the HaPO4-H202-H20 solution mentioned above. Radiation from an Nd 3 +:YAG laser at 1.06 pm was focused onto the cleaved input face of the fabricated samples. They operated as optical directional couplers. However, the breakdown voltage in these modulators was found to be much lower than that in the diodes described in Section 2. A modulation experiment could not be carried out. Improvement in the breakdown characteristics is urgently needed for the future development of this device. 4. CONCLUSIONS We have described a technique for the thermal diffusion of zinc into GaAs which was developed to produce a very thin p+ layer on a smooth surface of an nGaAs wafer. The diffusion was carried out by a closed-tube method at 580 °C for 2 h using a source of zinc plus ZnAs2. The thickness of the diffused layer was approximately 1.3 ~tm and the surface concentration of zinc was about 4.5 x 1019 cm- 3. The diffusion profiles were found to be stepwise, and this was explained using the theory of substitutional-interstitial diffusion. We also developed fabrication techniques for a coupled-waveguide optical modulator with a p-n junction in a strip-loaded channel-waveguide configuration, using an n/n ÷-GaAs wafer prepared by VPE with a thin diffused p+ surface layer. REFERENCES
1 E.A.J. Marcafili, BelISyst. Tech. J.,48(1969)2071. S. Kurazono, K. Iwasaki and N. Kumagai, Trans. Inst. Electron. Commun. Eng. Jpn., Sect. C, 55
2
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
(1972) 61. H.F. Taylor, J. Appl. Phys., 44 (1973) 3257. H. Kogelnik and R. V. Schmidt, IEEEJ. Quantum Electron., 12 (1976) 396. K. Tada and K. Hirose, Appl. Phys. Lett., 25 (1974) 561. K. Hirose, K. Tada and H. Yanagawa, Jpn. J. Appl. Phys., 16-S1 (1977) 311. K. Tada, H. Yanagawa and K. Hirose, Trans. Inst. Electron. Commun. Eng. Jpn., Sect. E, 61 (1978) 1. K.,Tada and H. Yanagawa , J. Appl. Phys., 49 (1978) 5404. K. Tada, H. Yanagawa and Y. Matsunaga, Jpn. J. Appl. Phys., 18-S1 (1979) 393. H. Kawaguchi, Jpn. J. Appl. Phys., 18-S1 (1979) 385. A. Carenco, L. Menigaux, F. Alexandre, M. Abdalla and A. Brenae, Appl. Phys. Lett., 34 (1979) 755. L.R. Weisberg and J. Blanc, Phys. Rev., 131 (1963) 1548.
L. L. Chang and G. L. Pearson, J. AppI. Phys., 35 (1964)1960. K.K. Shih, J. W. Allen and G. L. Pearson, J. Phys. Chem. Solids, 29 (1968) 379. B. Tuck, J. Phys. Chem. Solids, 30 (1969) 253. M . A . H . Kadhim and B. Tuck, J. Mater. Sci., 7 (1972) 68. B. Tuck and M. A. H. Kadhim, J. Mater. Sci., 7 (1972) 581.