Walter Schottky Institut and Physics Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany.
Nanotechnology. 2023 Feb 13;34(17). doi: 10.1088/1361-6528/acb4f6.
Nanostructures exhibit a large surface-to-volume ratio, which makes them sensitive to their ambient conditions. In particular, GaN nanowires and nanofins react to their environment as adsorbates influence their (opto-) electronic properties. Charge transfer between the semiconductor surface and adsorbed species changes the surface band bending of the nanostructures, and the adsorbates can alter the rate of non-radiative recombination in GaN. Despite the importance of these interactions with the ambient environment, the detailed adsorption mechanisms are still not fully understood. In this article, we present a systematic study concerning the environmental sensitivity of the electrical conductivity of GaN nanofins. We identify oxygen- and water-based adsorbates to be responsible for a quenching of the electrical current through GaN nanofins due to an increased surface band bending. Complementary contact potential difference measurements in controlled atmospheres on bulk- and-plane GaN reveal additional complexity with regard to water adsorption, for which surface dipoles might play an important role besides an increased surface depletion width. The sensitive reaction of the electrical parameters to the environment and surface condition underlines the necessity of a reproducible pre-treatment and/or surface passivation. The presented results help to further understand the complex adsorption mechanisms at GaN surfaces. Due to the sensitivity of the nanofin conductivity on the environment, such structures could perform well as sensing devices.
纳米结构具有较大的表面积与体积比，这使得它们对周围环境非常敏感。特别是 GaN 纳米线和纳米鳍会对环境做出反应，因为吸附物会影响其（光电）电子特性。半导体表面和吸附物种之间的电荷转移改变了纳米结构的表面能带弯曲，并且吸附物可以改变 GaN 中的非辐射复合速率。尽管这些与环境相互作用非常重要，但详细的吸附机制仍未完全理解。在本文中，我们对 GaN 纳米鳍的电导率对环境的敏感性进行了系统研究。我们确定氧和水基吸附物会导致 GaN 纳米鳍中的电流猝灭，这是由于表面能带弯曲增加所致。在控制气氛下对体 GaN 和平面 GaN 进行的补充接触电位差测量揭示了水吸附的额外复杂性，除了增加的表面耗尽宽度之外，表面偶极子可能会起到重要作用。电参数对环境和表面条件的敏感反应强调了需要进行可重复的预处理和/或表面钝化。所呈现的结果有助于进一步理解 GaN 表面的复杂吸附机制。由于纳米鳍电导率对环境的敏感性，此类结构可以作为传感设备发挥良好的性能。
