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A. E. Belyaev\ N. S. Boltovets^, V. N. Ivanov^, V. P. Kladko\ R. V. Konakova\ Ya. Ya. Kudryk\ A. V. Kuchuk\ O. S. Lytvyn\ V. V. Milenin\ Yu. N. Sveshnikov^ ^ V. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine 41 Nauki Prosp., Kiev, 03028, Ukraine e-mail: konakova@isp.kiev.ua, Ph.: +(380-44) 525-6182 ^State Enterprise Research Institute «Orion» 8a Eugene PottierSt, Kiev, 03057, Ukraine e-mail: bms@i.kiev.ua; Ph.: +(380-44) 465-0548 ^Close Corporation «Elma-I\^alakhit» Zelenograd, Russia

Abstract – We studied phase composition and parameters of the ohmic Au-TiBx-AI-Ti-n-GaN and barrier Au-TiBx-n-GaN contacts, both before and after rapid thermal annealing (RTA) at T = 870 °C for 30 s. The phase composition was studied with x- ray diffraction technique, while the parameters of the ohmic contacts were studied for the transmission line method (TLM) structures and those of the barrier contacts were studied by measuring the forward branches of f-V curves with further calculation of the Schottky barrier (SB) height фв and ideality factor n.

It was found that low-resistance (pc~ (1-3)x1 O’® Ω-cm^) ohmic Au-TiBx-AI-Ti-/7-GaN contacts can be formed using RTA. It turned out also that, after RTA at T = 870 °C for 30 s, the SB retains its barrier properties practically unchanged, as compared with the initial sample that has not been exposed to RTA.

I.                                    Introduction

Galllunn nitride is a wide-gap senniconductor that has been used in optoelectronics for nnany years [1]. Owing to the advances of new high technologies, a real possibility for developnnent of nnicrowave diodes and transistors on the basis of galliunn nitride and its solid solutions has appeared [2, 3]. The interest in such nnicrowave devices is aroused, first of all, by the fact that they nnake it possible to expand the operating tennperature range up to 800 °C. In this case, along with high heat resistance of the galliunn nitride nnaterial, still nnore stringent require- nnents are innposed upon the barrier-fornning and ohnnic contacts. In this connection the search for the adequate nnaterials for contact systenns continues up to now [2-6].

Earlier we have studied the ohnnic and barrier contacts (nnade with annorphous interstitial phases TiBx, ZrBx, NbNx, and TiNx) to the Si, GaAs, InP and SiC nnicrowave diodes. There were practically no interactions between phases in these contacts up to tennperatures nnore than twice the operating ones [7, 8]. In this work the previous experience was applied to fornnation of ohnnic and barrier contacts to the n-GaN epitaxial layers grown on sapphire (а-АЬОз).

II.       Sample and Experimental Procedure

Using photolithography, the planar Schottky diodes (SDs) were nnade on the n-GaN epitaxial filnn (thickness of -1 μηη, free charge carrier concentration of -10^^ cnn" ^) grown on sapphire. A Schottky barrier (SB) was nnade using nnagnetron sputtering of TiBx (up to a thickness of

0.      05 μηη) followed by sputtering of a gold nnetallization layer (contact layer) 0.2 μηη thick. The ohnnic contacts were prepared on the basis of Ti-AI-TiBx-Au nnetallization. The subsequently sputtered Ti (0.05 μηη) and Al (0.02 μηη) layers were exposed to rapid thernnal annealing (RTA): they were fired at a tennperature T = 870 °C for 30 s. After this the TiBx (0.1 μηη) and gold (0.2 μηη) layers were sputtered. The diode structure geonnetry is shown in Fig. 1.

Fig. 1. Layered structure of the contacts (a) and layout of the diode structure (b)

Ml. Result of Measurements

We took, both before and after RTA, the forward and reverse branches of I-V curves fronn which the SB height фв and ideality factor n were deternnined. The phase connposition of the contacts was studied with x- ray diffraction (XRD) technique for the AbOs-n-GaN-Ti- AI-TiBx-Au and AbOs-n-GaN-TiBx-Au test structures (before and after RTA). The XRD patterns for the AI2O3- π-GaN-TiBx-Au structures were studied ex-situ using an x-ray diffractonneter Philips X’Pert-MPD (Сика-radiation, wavelength λ = 0.15418 nnn) in the Bragg-Brentano geonnetry. The AbOs-n-GaN-Ti-AI-TiBx-Au structures were studied using a diffractonneter «Дрон-ЗМ».

The XRD patterns of the ohnnic contacts fornned using RTA (Fig. 2) have several peaks: (002) and (004) fronn the GaN epitaxial layer; (111), (200) and (220) from Au; (220) and (440) fronn AuGa2, (220) and (400) fronn TiN, (0006) and (0012) fronn AhOsand a «snneared» peak that seenns to stenn fronn the x-ray annorphous phases AlsTi and ΤΐΒχ. According to these results and the literature data, the ohnnic contact is fornned with a layer that appeared due to RTA near the Ti-GaN and Ti-AI interfaces in confornnity with the following reactions:

Ti + GaN ^ TiNx + GaNi_x and Ti + 3AI ^ AbTi.

The results of XRD studies presented in Fig. 2 correlate with the concentration depth profiles of the connpo-

nents of π-GaN-Ti-AI-TiBx-Au ohmic contacts that were obtained in [7] using Auger electron spectroscopy. The contact resistance for the TLM structures measured after RTA was (1-3)x10 ® Ω-cm^, i. e., more than two orders of magnitude below that in the initial samples.

Fig. 2. XRD patterns ofthe GaN-Ti-AI-TiBx-Au contact

The XRD patterns for the AbOs-n-GaN-TiBx-Au barrier contacts (taken both before and after RTA) (Fig. 3) have three peaks: (i) (0002) from the GaN epitaxial layer, (ii) (0006) from the а-АЬОз substrate, and (iii) from the Au (1^^) filnn. One can see from Fig. 3 that RTA at T =870 °C resulted in structural changes in the Au film only: an increase of the Au (111) peak height indicates presence of the [111] texture that is related to heat- induced increase of the gold grain size. The TiBx film is in the x-ray amorphous state, both before and after RTA. Formation of other phases due to the metallurgical processes in the metallization layers was not detected. This fact indicates thermal stability of these layers.

Fig. 3. XRD patterns ofthe Al203-n-GaN-TiB)^Au contact before (1) and after RTA atT= 870 ЯС for 30 s (2)

The above results were confirmed with measurements of SD l-V curves which practically did not change after RTA. The forward branch of the l-V curves of the Au-TiBx-n-GaN SDs taken both before and after RTA can be described with a single exponential portion, with SB height values of (0.8-1.2) V for different samples, and ideality factor values n « 1.34-1.68, respectively.

IV.                                    Conclusion

Thus our results show that RTA at Г = 870 °C leads to formation of heat-resistant ohmic contacts made on the basis of the Ti-AI-TiBx-Au metallization and does not change the parameters of the π-GaN-TiBx-Au barrier contacts.

[1]  Yu. G. Shretter, Yu. T. Rebane, V. A. Zykov, V. G. Sidorov. Wide-gap Semiconductors. Sankt-Peterburg: Nauka. 2001 (in Russian).

[2]  H. Marcos. Nitride Semiconductors and Devices. Berlin: Springer. 1999.

[3]  V. N. Danilin, Yu. P. Dokuchaev, T. A. Zhukova,

M. A. Komarov. New-generation high-power high- temperature-capable and radiation-tolerant microwave devices on the basis of wide-gap heterojunction AIGaN/GaN structures. Obzory po Elektronnoi Tekhnike. Ser. 1. SVCh Tekhnika. Moscow: GUP N11 «Pulsar». 2001 (in Russian).

[4]  P. Kordos. GaN-based Electronics: Material and Device Issues. Proc. ASDAM-2000. Smolenice Castle, Slovakia.

2000. p.47-54.

[5]  Mohamed S. Noor Contact mechanisms and design principles for alloyed ohmic contacts. J. Appl. Phys. 2004. v.95.

N 12. p.7940-7953.

[6]  N. A. Papanicolaou, K. Zekentes. High temperature characteristics of Ti/AI and Cr/AI ohmic contacts to n-type GaN. Solid-State Electron. 2002. v.46. p. 1975-1981.

[7]  A. E. Belyaev, N. S. Boltovets, V. N. Ivanov,

R. V. Konakova, Ya. Ya. Kudryk, P. M. Lytvyn, V. V. Milenin, Yu. N. Sveshnikov. Thermal stability of multilayer contacts formed on GaN. Pis’ma v ZhTF. 2005. v.31. N 24. p.88-94 (in Russian).

[8]  N. s. Boltovets, V. N. Ivanov, R. V. Konakova, Ya.

Ya. Kudryk, O. S. Lytvyn, P. M. Lytvyn, V. V. Milenin. Interactions between phases and the features of structural relaxation in the TiBx-n-GaAs (InP, GaP, 6H SiC) contacts exposed to active treatments. Fiz. Tekh. Poluprov. 2004. v.38.

N 7. p.769-774 (in Russian).


A.       E. Веляев\ H. 0. Волтовец^, В. Η. Иванов^,

B.       П. Кладько\ Р. В. Конакова\ Я. Я. Кудрик\

А. В. Кучук\ О. С. Литвин\ В. В. Миленин\

Ю. Н. Свешников^

^Институт физики полупроводников им. В. Е. Лашкарёва НАН Украины пр. Науки, 41, г. Киев, 03028, Украина e-mail: konakova@isp.kiev.ua; тел.: +{380-44) 525-6182 осударственное предприятие НИИ «Орион» ул. Эжена Потье, 8а, г. Киев, 03057, Украина e-mail: bms@i.kiev.ua, тел.: +{380-44) 465-0548 ЗАО «Элма-Малахит»

Зеленоград, Россия

Аннотация – До и после быстрой термической обработки (БТО) при Т = 870 °С в течение 30 с исследовались фазовый состав и параметры омических n-Au-TiBx-AI-Ti-n- GaN и барьерных Au-TiBx-n-GaN контактов. Фазовый состав исследовался методом рентгеновской дифракции, параметры омического контакта – на TLM структурах, барьерного – путем измерения прямых ветвей вольтамперных характеристик (ВАХ) и расчета из них высоты барьера Шоттки Фв и фактора идеальности п.

Установлено, что в результате БТО можно формировать низкоомные омические контакты Au-TiBx-AI-Ti-n-GaN с Рс ~ (1-3)х10 ® Ом см^. Оказалось также, что после БТО при Т = 870 °С в течение 30 с барьер Шоттки сохраняет барьерные свойства практически неизменными, по сравнению с исходным (не прошедшим БТО) образцом.

Источник: Материалы Международной Крымской конференции «СВЧ-техника и телекоммуникационные технологии», 2006г. 

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