Both n- and p-type doping have been achieved in GaN using Si{sup +} or Mg{sup +}/P{sup +} implantation, respectively, followed annealing at {ge} 1050{degrees}C. Using proximity rapid thermal annealing (10sec) the GaN surface retains both smooth morphology and its original stoichiometry. Variable temperature Hall measurements reveal approximate energy levels of 62meV for the implanted Si and 171meV for the Mg, which are similar to their values in epitaxially grown GaN. Implant isolation of both n- and p-type GaN, and n-type In{sub 0.75}Al{sub 0.25}N with multiple energy inert species (e.g. N{sup +} or F{sup +}) produces high resistivity ({ge}10{sup 8}{omega}/{open_square}) after subsequent annealing in the range 600-700{degrees}C. Smaller increases in sheet resistance are observed for In{sub x}Ga{sup 1-x}N (x=0.33-0.75) under the same conditions due to the smaller energy bandgaps and the shallower energy levels of the damage-related states controlling the resistivity

Abernathy, C. R.

Pearton, S. J.

Vartuli, C. B.

UNT Digital Library

.. DOPING AND ISOLATION OF GaN, InGaN AND InAlN USING ION IMPLANTATION S. J. Pearton, C. B. Vartuli, C. R. Abernathy and J. D. Mackenzie Department of Materials Science and Engineering University of Florida, Gainesville FL 3261 1 USA J. C. Zolper Sandia National Laboratories, Albuquerque NM 87185 USA C. Yuan and R. A. Stall EMCORE Corporation, Somerset NJ 08873 USA RECEf V F C  AUG 1 7 1% Abstract. implantation, respectively, followed annealing at 2 1050°C. Using proximity rapid thermal annealing (1Osec) the GaN surface retains both smooth morphology and its original stoichiometry. Variable temperature Hall measurements reveal approximate energy levels of 62meV for the implanted Si and l7lmeV for the Mg, which are similar to their values in epitaxially grown GaN. Implant isolation of both n- and p-type GaN, and n-type h0.75&.25N with multiple energy inert species (e.g. N' or F') produces high resistivity (210slY~) after subsequent annealing in the range 600-70O0C. Smaller increases in sheet resistance are observed for Infial-xN (x=0.33-0.75) under the same conditions due to the smaller energy bandgaps and the shallower energy levels of the damage-related stztes controlling the resistivity. Both n- and p - m e  doping have been achieved in GaN using Si+ or Mg'/P' 1. Introduction The recent realization of p-type doping of GaN during Metal Organic Chemical Vapor Deposition using Cp2Mg has led in a short period to the availability of blue and green light-emitting diodes [1,2]. The processing of these.devices could be improved if an implant doping technology was also practical, since one could employ selective area implantation for improved ohmic contact formation and moreover this would make possible a variety of field-effect transistor (ET) structures capable of high-temperature operation. Since ion implantation is a high yield, high throughput process, the availabilty of implant doping and isolation technologies would allow the production of FETs at a much lower cost than is currently possible with epitaxial growth. Junction FETs are for more readily fabricated using ion implantation of both n- and p-type dopants than would be the case with epitaxy, and integration of n-channel and p-channel devices is much simpler [3]. I DISCLAIMER I Thii report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof. nor any of their . employees, makes any warranty, express or implied, or assumes any legal liability or mponsi- f bility for the accuracy, completentss, or uscfuhess of any information, apparatus, product, or : process disclosed, or represents that its usc would not infringe privately owned rights. Refer- ., encc herein to any spccific commercial product, process, or service by trade name, trademark, ' manufacturer, or otherwise does not n d y  constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thenof. The views and opinions of authors expnss#l herein do not ntceSSarily state or reflect thosc of the United States Government or any agency thereof. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. To date, ion implantation has generally been used to introduce impurities for study of their optical properties [4]. GaN LEDs have been found to emit at 430nm (violet) when implanted with Mg, at 590nm (yellow) when Mg/Zn were co-implanted and in the green when implanted with Zn alone [5]. In all of the cases the implanted impurities behave as color centers. Implanted Er has also been reported to produce 1.54pm emission (from optically excited E?') in GaN [6]. In the FET structures reported by Binuri et al.(7,8], implantation with J3+ or He+ ions was used for device isolation. 2. Experimental The GaN layers used were grown on c-Al203 by MOCVD in a multi-wafer rotaing disc reactor at 1040°C with a GaN buffer layer of -2WA grown at 530°C. Undoped f h s  were n-type (I 4 ~ 1 0 ' ~ c m - ~ )  and were used for the doping experiments. Other layers were doped using disilane or biscyclopentadienyl-magnesium to achieve n- and p-doping, respectively of S 4~10'*cm-~. these samples were used for the implant isolation experiments. The hfial-xN (xd.33-1) and InxAll-xN (xd.5-0.75) were grown on semi-insulating GaAs by MOMBE between 525450°C using TEG, TMAAl and TMI for the group III elements and ECR generated nitrogen. The layers were auto-doped n-type ( 10'9-1020cm-3). The undoped GaN was implanted with Si' (5~10*~crn-~, 2OOkeV), Mg+(S~lO'~crn-~, 18OkeV) or Mg'/P'(5~10'~cm-~, 180/250keV) and annealed up to 1100°C for lOsec in a graphite susceptor. For isolation experiments, multiple energy (50- 250keV) N+, F' or 0' ions at doses of 2-50~10'~cm-~ were. used to produce uniform damage profiles throughout the nitride layers. Post-implant annealing at 400-900°C was employed to study the thermal stability of the isolation 3. Results and Discussion Figure 1 shows that above 1050"C, the implanted Si" becomes electrically active with an efficiency of -90% for a dose of 5~10 '~cm-~.  Mg+ implantation alone did not produce p- type doping, but when co-implanted with Pf we obtained a sharp n-to-p conversion of the GaN at 1050"C, with an activation efficiency of -60% at a dose of 5~10 '~cm-~ .  As in other IU-V semiconductors, the role of the P' co-implant is to increase the vacancy concentration and promote substitutionality of the Mg upon annealing. Annealing by itself above 1000°C produced a slight increase in n-type conductivity in GaN which may be a result of creation of Nv-related centers. Variable temperature Hall measurements on the implanted samples showed activation energies of -62meV for Si (Figure 2) and -17lmeV for Mg (Figure 3) similar to their values in epitaxially grown material [9,10]. We note however that these are dependent on the method of plotting the data and if one uses p y a  instead of Ns, then values of 30 and 120meV are obtained. Both n- and p-type GaN can be converted to high-resismce material (>109Q / O )  by N' implantation and subsequent annealing at -750°C where hopping conduction is minimized. Activation energies of -0.9OeV for initially n-type, and 0.83eV for initially p- type GaN, were obtained from temperature-dependent resistivity measurements, suggesting the Fermi-level becomes pinned at these energies in isolated material. These .. values are not at midgap (-1.6eV), which is the most favorable situation for achieving maximum isolation resistances, but are still large enouzh that the GaN resistivity is well above the minimum necessary for good electronic device isolation, i.e. >106Q /O (1 11. F . . . I . I . 'e  1 700 800 900 1000 1100 Anneal Temperature ("C) Figure 1. Sheet resistance of nominally undoped GaN either unimplanted. or implanted with a dose of 5~1O '~cm~~Si+ ,  MgT or Si+, Mg+, as a function of annealing temperature. y -  4.3291=+14 e*(-1.9858x) R- 0.88206 1 ° 1 3 1  - l O " I . . . ' " . '  ' " " " " " ' . " . . . I  28 3 32 3.4 3.6 3.8 4 4.2 1 ooorr (K1) Figure 3. Arrhenius plot of carrier density in Mg'ip' implanted GaN. 10" -. , . . ,.. . . , . . . .  , , . . . ,. . . .  , , . . . , . . . . I  . . . .  - y = 4.3994e+14 eA(4.71367~) R- 0.99809 1013 I -r ! 5 zs I 1 0 l 2  1 i I v I loll i , , ,,,. .., ,, , , ,. . , , ,, ., ,,., , , , ,  , ,A 3 4 5 6 7 8 9 1 0 1 1  l O 0 O r r  (K-l) Figure 2. Arrhenius plot of carrier density in Si+ Figure 4. Normalized sheet resistance (relative to the unimplanted values) versus anneal temperature for Ino.75Alo.z_cN implanted With various doses of o+. For the ternary compounds, increases in sheet resistance of up to a factor of -lo4 were achieved in h0.75&.25N after implantation at high doses (-10'4~m-2) of the isolating species, followed by annealing at 600-70O0C (Figure 4). Slightly lower increases were obtained for mediums (-10'3cm-2) or low (-1012cm-2) doses. The behavior for Infial-xN followed the same general trends, with somewhat lower increases in sheet resistance h0.75&.& the Fermi level appears to pin at Ec-0.54eV for high N'+ doses and &- 0.19eV for low doses, whereas in h0.33GQ.67N optimized annealing conditions produce a dominant activation energy of only 0.40eVY and above gn annealing temperature of . .  I .  -800°C the energy level reverts to w . 0 2 5 e V  (the same as in the as-grown material). There was no evidence for a high density of chemical deep levels associated with the implanted N+, F' or 0'. The implant isolation behavior of n-type InGaN and InAlN appears analogous to that of InP and InGaAs in that only moderate resistivities are obtainable in initially n-type material. * 4. Summary For electronic device isolation it appears that JnxAll-xN can be made sufficiently resistive by implantation, whereas the initial conductivity of InxGal-xN will determine whether or not implantation will be successful for isolation. For photonic devices, the requirements are less demanding and implantation should work well for current guiding. In GaN implant isolation works quite well in both n- and p-type material. We have achieved good implant activation by the simple expedient of using a high annealing temperature and high quality starting material. Acknowledgments The work at UF is partially supported by grants from NSF ( Division of Materials Research, DMR 95-36533), an OWARPA University Research Initiative (N00014-92-J- 1895) and an AASERT grant through ARO (Dr. J. M. Zavada). The staff of the Microfabritech facility is gratefully acknowledged. The work at Sandia is supported by the US Department of Energy under contract no. DE-ACW94AL85000, and the technical help of J. Escobedo is greatly appreciated. The work at EMCORE is supported by BMDO-15T under contract NOOO14-93-C-6269) managed by M. Yoder at ONR. The EMCORE authors greatly appreciate the assistance of T. Salagai, M. Schurman and C. Y. Hwang. References [l] Nakamura S., Mukai T. and Senoh M. 1994 Appl. Phys. Lett. 64 1687 ; 1994 J. Appl. Phys. 76 8189 [2] Akasaki I., H. Ammo, Kito M. and Hiramatsu K., 1991 J. Lumin 48/49 666. [3] Zolper J. C., Shervin M. E., Baca A. G., Shul R. J., Klem J. E and Hietala V. M. 1994 IEEE Electron. [4] Pankove J. I. and Hutchky J. A. 1976 J. Appl. Phys. 47 5387. [SI Muruska H. P. and Tiefjen J. J., 1969 Appl. Phys. Lett. 15 327. [6] Wilson R. G., Schvartz R. N., Abernathy C. R., Pearton S. J., Newanan N., Rubin M., Fu T. and Dev. Lett. EDL -15 493 Zavada J. M. 1994 Appl. Phys. Lett. 65 992 Electronics Lett. 30 1248 Sept 1994 Roc 1994 Int. Symp. Comp. Sernicond. (in press)-held in San Diego CA. Phys. Lett. 65 593 [A Binari S. C., Rowland L. B., Kruppa W., Kelner G., Doverspike K. and Gaskill D. K. 1994 [8] Binari S. C., Rowland L. B., Kelner G., Kruppa W., Dietrich H. B., Doverspike K. and Gaskill D. K. [9] Tanaka T., Watanabe A., Amano H., Kobayashi Y.. Akasaki I., Yanazaki S .  and Koike M. 1994 Appl. [lo] Kim J. G., Frenkel A. C., Liu H. and Park R. M. 1994 Appl. Phys. Lett. 65 91 E1 11 Pearton S. J. 1990Mat. Sci. Eng. Rep. 4 313 

Doping and isolation of GaN, InGaN and InAlN using ion implantation

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Doping and isolation of GaN, InGaN and InAlN using ion implantation

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