Influence of unintentional doped carbon on growth and properties of N-doped ZnO films

Abstract

Articles you may be interested inThermal diffusion of nitrogen into ZnO film deposited on InN/sapphire substrate by metal organic chemical vapor deposition Electrical and optical studies of metal organic chemical vapor deposition grown N-doped ZnO films Unintentional doping and compensation effects of carbon in metal-organic chemical-vapor deposition fabricated ZnO thin films The evolution of optical and electrical properties induced by rapid thermal annealing is studied on nitrogen-doped ZnO samples grown by metal-organic chemical vapor deposition ͑MOCVD͒. Correspondingly, in the Raman spectra carbon cluster related D and G modes have been observed to increase with annealing temperature. The increase in the intensity ratio of D and G modes indicates growing of carbon clusters, revealing an interesting change in unintentional doped carbon, which is a popular impurity in MOCVD grown N-doped ZnO. Substitutional or interstitial carbons in the grains may migrate to grain boundaries to incorporate with some existing carbon clusters to form larger ones. Accordingly, zinc vacancies will then be easily formed as annealing temperature increased, resulting in eminent green band emission at room temperature photoluminescence. The band edge emissions also show significant changes with several shoulders observed by thermal annealing, which can be ascribed to acceptor or donor related emissions. The changes in emissions agree well with the evolution of the electrical property of annealed samples. This study shows that unintentional doped carbon has a great influence on ZnO growth by forming clusters in the grain boundary area and also on the optical and electrical properties by forming C related defects in the grains.

SIMS and Raman characterizations of ZnO:N thin films grown by MOCVD

“…The contribution of nitrogen carrier gas is not excluded on the appearance of the broad mode at 515 cm À 1 , which disappeared after annealing. Similar band was also observed by Chen et al [19] in nitrogen doped ZnO films grown by MOCVD on sapphire substrate. The second order Raman scattering appears at high frequency (1000-1200 cm À 1 ).…”

“…N O ), and most probably the incorporation of N in the ZnO matrix, measured by SIMS, is related to defects complexes involving N. In doped samples S 1 and S 2 , or undoped film S 2 À ND grown with oxygen deficiency, the presence of defect complexes such as (N 2 ) O , CN, N 2 O, Zn-H and carbon clusters is accompanied by a breakdown of the translational symmetry that causes the well-known ZnO phonon modes to disappear. In addition, some of these complexes are known as shallow donors in ZnO and may cause easily compensation of the acceptors [19,20]. If one correlates with Hall-effect measurements presented in Table 1, this may explain the n-type conductivity and the strong electron concentration of the samples.…”

“…Based on previous works on nitrogen-pair oxygen defects this mode was attributed to the presence of N 2 O defects [24]. Another peak located around 1980 cm À 1 , attributed to Zn-H complexes [19,21], appears in the Raman spectrum of the film S 2-ND grown at R VI/II ¼0.5. It is also interesting to note that no particular local vibrational modes (LVM) of nitrogen can be observed in the doped films grown using N 2 as carrier gas.…”

“…Raman spectroscopy revealed the presence of carbon complexes and clusters [19,20]. Previous studies found that high temperature annealing and rather high growth temperature caused a decrease in nitrogen concentration while the carbon concentration remained constant [19,21].…”

A brief review of co-doping

“…Experimentally, it was reported that C sp2 clusters, which are graphite-like along grain boundaries [220,221], were found in undoped [217,222] and N-doped ZnO [216,221,222]. This indicated that defect complexes of CH x , NH x , and NC x were likely to be present [193], with C concentration significantly increasing in N-doped samples [193,223,224].…”