Separating the Contributions of Hydrogen and Structural Relaxation to Damage Annealing in a -Si:H
- PDF / 445,410 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 112 Downloads / 188 Views
SEPARATING THE CONTRIBUTIONS OF HYDROGEN AND STRUCTURAL RELAXATION TO DAMAGE ANNEALING IN a-Si:H P.A. STOLK,a A.J.M. BERNTSEN,b F.W. SARIS,a and W.F. VAN DER WEGb a FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands. b Debye Institute, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands.
ABSTRACT This paper investigates the effects of ion implantation and annealing for pure (a-Si) and hydrogenated amorphous silicon (a-Si:H). The photocarrier lifetime in as-deposited a-Si:H 14 2 decreases from Ž200 to 3 ps after 1 MeV Si+ implantation to doses exceeding 10 /cm . A comparison with relaxed a-Si suggests that damage generation in a-Si:H merely arises from displacements in the silicon network. Annealing of ion-damaged a-Si:H at 200-500 TC recovers the carrier lifetime to 60-100 ps as a result of hydrogen passivation of electrical defects. However, Raman spectroscopy shows that hydrogen does not significantly enhance long-range network relaxations during annealing. This implies that thermal treatments of ion-implanted a-Si:H can not fully recover the as-deposited state. INTRODUCTION Ion implantation is widely used to introduce dopants into semiconductors. It has been suggested that ion implantation is also suitable for doping hydrogenated amorphous silicon (a-Si:H) [ 1]. The accumulation of implantation damage in a-Si:H requires annealing treatments to recover the electrical properties of the material and to achieve dopant activation [2]. However, the process of damage annealing in a-Si:H is still not well understood. On the other hand, the annealing behavior of pure amorphous silicon (a-Si), prepared by ion-beam-amorphization of crystalline silicon (c-Si), has been extensively investigated in the past few years [3,4]. Raman spectroscopy has shown that the average bond-angle distortion in the a-Si network decreases upon thermal annealing below the crystallization threshold [5,6]. This process is also known as structural relaxation. Further evidence for structural relaxation of a-Si was given by differential scanning calorimetry [7]. Structural relaxation is accompanied also by the annihilation of point defects in the a-Si network, a process similar to damage removal in ion-implanted c-Si [3]. Recently, we have shown that the photocarrier lifetime in a-Si increases from =1 ps to =10 ps during relaxation, which is consistent with the idea of annealing out electrically active defects [8]. Conversely, introducing defects in relaxed a-Si by ion irradiation returns the material to the as-implanted state [3,8,9]. In the present paper, the formation and annealing of ion damage in a-Si:H and a-Si is compared. The samples are characterized by photocarrier lifetime measurements and Raman spectroscopy, which serve as probes for electrical defects and structural disorder, respectively. This study enables a separation of the contributions of hydrogen and structural relaxation to damage annealing in a-Si:H. EXPERIMENT 2 Pure a-Si layers were prepared by implanting 8Si ion
Data Loading...
