Department of Materials Science and Engineering, ‡Department of Physics, and §Department of Electrical Engineering and Computer Science, University of Michigan , Ann Arbor, Michigan 48109, United States.
Nano Lett. 2017 Dec 13;17(12):7853-7858. doi: 10.1021/acs.nanolett.7b04122. Epub 2017 Dec 4.
We investigate hybrid charge transfer exciton (HCTE) confinement in organic-inorganic (OI) quantum wells (QWs) comprising a thin InGaN layer bound on one side by GaN and on the other by the organic semiconductors, tetraphenyldibenzoperiflanthene (DBP) or 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP). A binding energy of 10 meV is calculated for the Coulombically bound free HCTE state between a delocalized electron in GaN and a hole localized in DBP. The binding energy of the HCTE increases to 165 meV when the electron is confined to a 1.5 nm InGaN QW (HCTE). The existence of the HCTE is confirmed by measuring the voltage-dependent DBP exciton dissociation yield at the OI heterojunction in the QW devices that decrease with increasing In concentration and decreasing electric field, matching the trends predicted by Poole-Frenkel emission. Combining spectroscopic measurements with optical models, we find that 14 ± 3% of the excitons that reach the GaN/DBP heterojunction form HCTEs and dissociate into free charges, while the remainder recombine. A high nonradiative recombination rate through defect states at the heterointerface account for the lack of observation of HCTE photoluminescence from GaN/InGaN/CBP QWs at temperatures as low as 10 K.
我们研究了由 GaN 一侧和有机半导体四苯并二苯并对二呋喃（DBP）或 4,4'-双（N-咔唑基）-1,1'-联苯（CBP）另一侧组成的有机-无机（OI）量子阱（QW）中的混合电荷转移激子（HCTE）限制。计算了在 GaN 中离域电子和 DBP 中局域空穴之间的库仑束缚自由 HCTE 态的结合能为 10 meV。当电子被限制在 1.5nm InGaN QW 中时，HCTE 的结合能增加到 165 meV（HCTE）。通过在 QW 器件中测量 OI 异质结处的电压依赖的 DBP 激子离解产率来确认 HCTE 的存在，该产率随 In 浓度的增加和电场的减小而减小，与 Poole-Frenkel 发射预测的趋势相匹配。结合光谱测量和光学模型，我们发现，在到达 GaN/DBP 异质结的激子中，有 14±3%形成 HCTE 并离解成自由电荷，而其余的激子则重新复合。由于异质界面处的缺陷态导致非辐射复合速率很高，因此在低至 10 K 的温度下，无法观察到 GaN/InGaN/CBP QW 中的 HCTE 光致发光。
