蓝色发光GaN纳米晶和晶体的XAFS研究

利用XSAFS（X－射线吸收精细结构）方法研究六方的纳为晶和晶体GaN在78K和300K温度下Ga原子的局域配位环境结构，对于第一近邻Ga－N配位，纳米晶GaN的平均增长R、配位数N、热无序度σT和结构无序度σs与晶体GaN的相近，分别为0．194nm、4．0、0．0052nm、0．0007nm；当温度从78K增加到300K，GaN样品中Ga－N配位的σT增加不多，小于0．0005nm，表明第一近邻Ga－N配位的共价键作用力较强，几乎不受温度和晶体状态的影响。对于第二近邻Ga-Ga配位，R为0．318nm，纳米晶GaN的σs（0．0057NM）比晶体GaN的（0．001nm )大0．0047nm；在78K和300K时，纳米晶GsA样品的Ga-Ga位位的σT分别为0．0053nm和0.0085nm，这一结果表明Ga-Ga配位的σT受温度变化产生很大影响，纳米晶GaN中Ga原子的局域配位环境与晶体GaN的差别主要表现在第二近邻Ga-Ga配位的σs相对较大，可能是由于纳米晶GaN内部缺陷及存在较多的表面不饱和配位原子所致。

XAFS STUDIES ON LOCAL STRUCTURES OF NANOCRYSTALLINE AND CRYSTALLINE GaN '

X-ray absorption fine structure (XAFS) was use d to investigate the local structures around Ga atoms in the hexagonal nanocryst alline and crystalline GaN under 78K and 300K. For the first nearest-neighbor c oordination of Ga-N, the average bond length R, coordination N, thermal disorder σT and structural disorder σS of nanocrystalline GaN ar e similar to those of crystalline GaN, which are 0.194nm, 4.0,0.0052nm and 0.000 7nm, respectively. When the temperature is elevated from 78K to 300K, the σ T in GaN samples increases by lower than 0.0005nm. It indicates that the Ga- N covalent bond is much stronger, and is nearly independent of temperature and c rystalline state. For the second nearest-neighbor Ga-Ga coordination, the R values of the samples are about 0.318nm; the σS(0.0057nm) of nanocryst alline GaN is 0.0047nm larger than that of crystalline GaN(0.001nm); the σT of Ga-Ga coordination in nanocrystalline GaN are 0.0053nm, 0.0085nm for the temperature of 78K and 300K, respectively. This shows that the σT of Ga- Ga coordination is greatly affected by the temperature. The major difference of local structure around Ga atoms between nanocrystalline GaN and crystalline GaN is shown by the relatively large σS of the Ga-Ga second nearest-neighbo r shell in nanocrystalline GaN. The reason may be explained by that there exist larger defects and unsaturated surface atoms in nanocrystalline GaN.