Electrical activation acceptors

Electrical measurements, mainly temperature-dependent Hall-effect measurements, have been critical in the elucidation of donors and acceptors in ZnO. The main background donors in state-of-the-art VP-grown ZnO have been shown to be H and Al, and the acceptor, Vzn. Other possible donors that must be investigated further are the defects Vo and Znj. Although Vzn seems to be the main electrically active acceptor, still N is evidently present at a much higher concentration. If this is true, then N must be passivated, and the likely passivator is H. Indeed, annealing experiments lead to a much higher acceptor concentration, presumable due to the... 

In a semiconductor, substitutional FAs from the same column of the periodic table as the one of the crystal atom they replace are usually electrically inactive and they are called isoelectronic with respect to the semiconductor. It can occur, however, that for some isoelectronic impurities or electrically-inactive complexes, the combination of the atomic potential at the impurity centre with the potential produced by the local lattice distortion produces an overall electron- or hole-attractive potential in a given semiconductor. This potential can bind an electron or a hole to the centre with energies much larger than those for shallow electrically-active acceptors or donors. The interaction of these isoelectronic impurities traps the free excitons producing isoelectronic bound excitons which display pseudo-donor or pseudo-acceptor properties. This is discussed later in this chapter in connection with the bound excitons, and examples of these centres are given in Chaps. 6 and 7. 

Acceptor doping density Number of electrically active acceptors per volume ( /cm ). 

Besides the electrically active complexes discussed above, there is indirect evidence for the existence of neutral complexes. In close analogy to the observations in silicon and several III-V materials it appears that hydrogen passivates deep and shallow acceptors. Because of the small concentrations of these neutral centers, all attempts to detect them directly with local vibrational mode (LVM) spectroscopy or electron paramagnetic resonance (EPR) have been unsuccessful. 

Before discussing the redistribution of implanted dopants in GaN, it is necessary to briefly review the temperatures required to achieve electrical activity. Pearton et al reported that a temperature of 1100°C is required to achieve electrical activation of Si and Mg + P in GaN [3], However, this temperature is not sufficient to completely remove the implantation induced damage [4], To completely restore the crystal lattice, an annealing temperature of between 1250°C and 1600°C will be required [5], Most of the results on donor redistribution have been for anneals near 1100°C, as discussed in the following sections however, more experimental work must be done at the higher temperatures to characterise the effect of these higher temperatures. The following discussion is separated into common donor impurities (Si and O) and acceptor impurities (Be, Mg, Zn and Ca) in GaN. 

Many other methods have been employed to study CTC in biological systems, such as calorimetry, mixed fusion analysis, solubility and partition methods, ultrasonic methods, spectropolarimetry, reflective infrared spectroscopy, Raman spectroscopy, flash photolysis spectroscopy, nuclear quadrupole resonance spectroscopy, and magnetic susceptibility methods, to name several of a very long list. X-ray photoelectron spectroscopy (XPS) has also been used to elucidate some EDA interactions in electrically active macromolecules. XPS is useful for detecting the redistribution of charges in complexes of such compounds, (e.g., in the presence of phosphate acceptors, the nature of the semiconductive environment of S, O, and N bridges in macromolecules is affected profoundly [111]. 

---