Sarkar Shaibal K, Cohen Hagai, Hodes Gary
Department of Materials and Interfaces, The Weizmann Institute of Science, Rehovot 76100, Israel.
J Phys Chem B. 2005 Jan 13;109(1):182-7. doi: 10.1021/jp046485l.
If a thin film (tens of nm) of CdSe quantum dots (4 nm diameter) is deposited by chemical bath deposition onto various substrates, the films, although essentially intrinsic, behave as if they were n-type with respect to charge separation. However, films deposited under certain deposition conditions on Si (both n(+)- and p(+)-type) behave as if they were p-type. In this case, we show that it is possible to switch this p-type photoresponse by either light illumination intensity or injection of electrons from an external filament. Using both surface photovoltage spectroscopy and a novel adaptation of X-ray photoelectron spectroscopy, we show how this behavior results from a Cd(OH)(2) layer adsorbed at the Si surface at the beginning of the deposition. This response is explained by a competition between a high concentration of relatively shallow hole traps in the CdSe and a lower concentration of deeper electron traps in the Cd(OH)(2). The relative occupancies of these traps determine the fields in the film and their response to external parameters.
如果通过化学浴沉积法将直径为4纳米的CdSe量子点的薄膜（几十纳米）沉积在各种衬底上，这些薄膜虽然本质上是本征的，但在电荷分离方面表现得好像是n型的。然而，在某些沉积条件下沉积在Si（n(+)型和p(+)型）上的薄膜表现得好像是p型的。在这种情况下，我们表明可以通过光照强度或从外部灯丝注入电子来切换这种p型光响应。利用表面光电压光谱和X射线光电子能谱的一种新颖改进方法，我们展示了这种行为是如何由沉积开始时吸附在Si表面的Cd(OH)₂层导致的。这种响应可以通过CdSe中相对浅的空穴陷阱的高浓度与Cd(OH)₂中较深的电子陷阱的较低浓度之间的竞争来解释。这些陷阱的相对占有率决定了薄膜中的电场及其对外部参数的响应。
