25E08
Study on ZnO source using non-neutral plasma trap
非中性プラズマトラップを用いた酸素脱離のない ZnO 源の研究
Haruhiko Himura, Yuji Nishioka, Takashi Okamoto,Kiyonori Hirota, Akio Sanpei, and Sadao Masamune
比村治彦，西岡祐司，岡本 崇，廣田聖典，三瓶明希夫，政宗貞男
Department of Electronics, Kyoto Institute of Technology
Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
京都工芸繊維大学・電子システム工学専攻 〒606-8585 京都市左京区松ヶ崎御所海道町
As one of applications of our Penning-type trap having both positive and negative electrostatic potential
wells, we consider to use it to make the semiconductor ZnO, especially pure ZnO clusters or perhaps
quantum dots for p-type conduction. Several numerical calculations are performed (Y. Nishioka, H. Himura
et al., 24G15 in this conference.) Regarding the experimental machine, an equipment that introduces
oxigen gas into the vacuum chamber is now ready. A source of zinc particles, on the other hand, is still
under consideration. Principles and objectives of this proposed project are explained.

1. Next generation compound semiconductor
GaN and ZnO are compound materials that are
categorized in wide band gap semiconductors. In theresearch field of GaN, plasma processing has alreadybeen recognized as one of key technologies.
As for ZnO, during the last several decades, opticalproperties and processes in zinc oxide (ZnO) as wellas its refractive index have been extensively studied.
Recently, the renewed interest in ZnO has been fuelled
and fanned by prospects of its potential applications in
optoelectronics owing to its direct wide band gap (Eg~ 3.3 eV at 300 K), large excitation binding energy (~60 meV), and efficient radiation recombination.
For the purpose of developing new optical devices
such as a blue light-emitting diode (LED) that iscomposed of ZnO-based structures with no use of rare
metals, ZnO is required to grow into a uniform size ofhigh-quality bulk ZnO cluster that has a unit of about(ZnO)n=1000 structure with low impurity concentration.
2. Inherent problems of current processing
Although many reports dealing with deposition ofZnO have utilized industrial growth techniques suchas magnetron sputtering with/without radio frequency(RF), chemical vapor deposition (CVD), they allow nocontrol of ZnO particles over the deposition procedure,probably too insufficient to produce uniform andhigh-quality ZnO bulk clusters. Other methods ofmolecular beam epitaxy (MBE) and pulsed laser
deposition (PLD) and so on are also extensively
applied, depending on the chemistry used. However,any mechanical pieces provided for those facilities arehardly cheap, which is obviously unfavorable if weintend to apply those to industrials. Also, since in all
methods working gases are directly introduced invacuum reactors, we can never avoid difficulties due
to residual background neutrals. A new method for thegrowth of ZnO clusters is thus called for.

3. The proposed experiment; Penning-type
non-neutral plasma trap may work as a newplasma processing
In our laboratory, we have constructed a new
Penning-type trap that contains a pair of positive
and negative electrostatic potential wells in thevacuum chamber [1]. Also, the electric field alongwith the bias magnetic one (~ 1 kG) is completelystatic. Thus, any heating of charged particles due toAC electric field is never caused, which, in fact, may
be a possible reason why larger Si clusters beyond n =10 were never produced in a Paul trap [2].
The Penning-type trap may work as new plasma
processing without impurity. If an ionized ZnO
particle (ZnO+) or just Zn+ along with neutral ZnO
particles can be externally injected into the static
fields, the injected ZnO+ or Zn+ would be trapped in
the bottom of positive potential well for a long time
according to the conservation of angular momentum.
On the other hand, in the bottom of negativeelectrostatic potential well, negative oxygen ions Oor O2- could be confined. Those charged particles
attract each other, and moreover, the ion cluster does
even neutral species of ZnO, too. Finally, those may
grow into a (ZnO)n cluster via a condensation process.
In order to test the possibility of the Penning-type
non-neutral plasma trap, we plan to perform several
preliminary experiments. In this conference, we will
discuss principles and objectives of those experiments.

References[1] Y. Nishioka et al., 22C01 in this conference.
[2] H. Murakami and T. Kanayama, Appl. Phys. Lett. 67,(1995) 2341.