Fabrication of As-doped p-type ZnO thin film and ZnO nanowire inserted p-n homojunction structure

Manoj Kumar, Jyoti Prakash Kar, In Soo Kim, Se Young Choi, Jae Min Myoung

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

Arsenic-doped p-type ZnO (ZnO:As) thin films were grown on Si (100) wafer by E-beam evaporation. As-grown ZnO:As film exhibited n-type conductivity whereas on annealing the conduction of ZnO:As film changes to p-type. X-ray photoelectron spectroscopy show that the bonding state of arsenic in ZnO:As film is present in As-O state. ZnO homojunction synthesized by deposition of Al-doped n-type ZnO and intrinsic nanowire ZnO on As-doped p-type ZnO showed clear p-n diode characteristics. The neutral-acceptor bound exciton (A 0X) and donor-acceptor-pair (DAP) emissions in the low temperature photoluminescence studies further support the p-type conduction in ZnO:As.

Original languageEnglish
Pages (from-to)689-692
Number of pages4
JournalApplied Physics A: Materials Science and Processing
Volume97
Issue number3
DOIs
Publication statusPublished - 2009 Nov

Bibliographical note

Funding Information:
tryptic peptides, derived from the purified enzyme, were sequenced and these peptide sequences, denoted by the underlining in Fig. 3, were identical to those deduced from the nucleotide sequence. The sequence of the spinach enzyme is 83% identical with that of the maize enzyme \[13\]a t the amino-acid level. By comparison of the spinach and maize sequences, it appears that the 4948 base pairs sequenced include 98% of the coding sequence of the 1483 amino-acid-long mature spinach enzyme. Approximately 103 bp, coding for the 34 amino acids at the amino-terminus of the mature protein are missing from the clones we have isolated. Attempts to obtain a cDNA that includes the 5'-end of the transcript, i.e., the portion that encodes the missing portion of the mature protein and the transit peptide \[13\]b, y screening additional libraries with both spinach and maize probes and by using linker-primed PCR \[19\] were all unsuccessful. However, the sequence of 23 amino acids at the amino-terminus, from amino acid 2 to amino acid 24, of the mature spinach enzyme was determined by sequencing the purified enzyme. In addition, analysis of the amino-terminus sequencing data suggests that cysteine is likely to be the N-terminal amino acid of the spinach enzyme, as is the case for the maize enzyme \[13\]b, ut this could not be established unambiguously. The sequence for amino acids 2 through 24 of the spinach enzyme is GVGFI-ANLDNKGSFQIVKDALTA. If, as appears likely, cys-teine is at the amino termini of both the spinach and maize enzymes, the two enzymes are identical at 17 of the first 25 positions. Despite the fact that the spinach and maize enzymes use reduced ferredoxin as the electron donor, while bacterial enzymes use NADPH, considerable homology exists between the two higher plant enzymes and the large subunits of bacterial glutamate synthases for which sequences are known. Thus, at the amino-acid level the spinach enzyme is 43.3% identical to the large subunit of the NADPH-dependent glutamate synthase of Azospirillum brasilense \[20\]a nd 39.1% identical to the large subunit of the E. coli enzyme \[21\]. A comparison of the sequence of the spinach ferredoxin-dependent glutamate synthase with those of the A. brasilense and E. coli NADPH-dependent glutamate synthases and to the sequences of the glutamine ami-dotransferases of Bacillus subtilis and Rhizobium leguminosarum (See discussion in Ref. 20) suggests that the glutamine amidotransferase domain of the spinach enzyme lies within the amino-terminal 350 residues. A similar comparison of the spacing of cysteine residues in the spinach enzyme to those found in the maize, A. brasilense and E. coli enzymes and to those found in E. coli fumarate reductase and B. subtilis succinate dehydrogenase (see discussion in Ref. 20) suggest that cysteines 1097, 1103 and 1108 function as ligands to the \[3Fe_4S\]1+ ,0 cluster (Note that the amino-acid position numbers assigned to spinach glutamate synthase in this discussion and below are those taken from Fig. 3 and the precise numbering of amino-acid residues must await the completion of the sequence.) A comparison of the sequence of the spinach enzyme to those of other glutamate synthases and those of Saccharomyces cerevisia flavocytochrome b 2, spinach glycolate oxidase, and Hansenula anomola flavocytochrome b 2 (see discussion in Ref. 20) suggest that the FMN-binding domain of the ferredoxin-dependent spinach glutamate synthase lies between residues 975 and 1097. A similar analysis suggests that the FAD-binding domain of the spinach enzyme may involve amino acids in the region between residues 1278 and 1288 or between residues 1345 and 1398. The authors would like to thank Ms. Ida Schaefer and Dr. Susan San Francisco for their synthesis of oligonucleotides, Dr. Susan Abrahamson and Dr. W. Gruissem for providing the spinach cDNA library, Dr. Toshiharu Hase for providing a full-length cDNA clone of maize glutamate synthase and Dr. Clive Slaughter for his advice on the amino-acid sequencing of the peptides. This work was supported by grants from the U.S. Department of Energy (DE-FG05-90ER20017 and 93ER20125 to D.B.K.). The oligonucleotide syn-thesis facility is supported by the Texas Tech Univer-sity Institute for Biotechnology.

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Materials Science

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