$β-Ga_{2}O_{3}$击穿极限的光谱测量及自陷激子和空穴的隧道电离
Spectral measurement of the breakdown limit of $β-Ga_{2}O_{3}$ and tunnel ionization of self-trapped excitons and holes
摘要：
$β-Ga_{2}O_{3}$是一种不寻常的半导体，其中可以施加大的电场（~1-6 MV/cm），同时仍然保持在其超宽带隙以下的主要激子吸收峰。这提供了一个难得的机会，在固态研究激子和载流子自陷动力学在强场极限在稳态。在亚带隙光子激发下，我们观察到与激子吸收相关的光谱光电流峰的场致红移和与自陷空穴电离相关的高场下峰振幅的阈值样增加。依赖于场的光谱响应与eXciton修改的Franz-Keldysh（XFK）效应模型定量拟合，该模型包括由于二次斯塔克效应而导致的依赖于电场的激子结合能。在介电击穿开始时，精确地观察到具有反向偏压的光谱红移的饱和，从而提供了检测和量化局部电场和介电击穿行为的光谱手段。此外，依赖于场的响应度提供了对光电流产生途径的洞察，揭示了自陷激子（STX）和自陷空穴（STH）的光电流贡献。通过激子和自陷空穴的场依赖隧道电离定量解释了$β-Ga_{2}O_{3}$中的光电流和p型输运。我们采用STX和STH的场相关隧道电离的量子力学模型来模拟光电流振幅的非线性场相关性。拟合的数据，我们估计的有效质量的价带空穴$(18.8 m_{0})$和超快自陷时间的空穴（0.045 fs）。这表明，少数空穴输运$β-Ga_{2}O_{3}$只能通过隧道电离的STH在强电场下产生。
英文摘要：
$β-Ga_{2}O_{3}$ is an unusual semiconductor where large electric fields (~1-6 MV/cm) can be applied while still maintaining a dominant excitonic absorption peak below its ultra-wide bandgap. This provides a rare opportunity in the solid-state to examine exciton and carrier self-trapping dynamics in the strong-field limit at steady-state. Under sub-bandgap photon excitation, we observe a field-induced red-shift of the spectral photocurrent peak associated with exciton absorption and threshold-like increase in peak amplitude at high-field associated with self-trapped hole ionization. The field-dependent spectral response is quantitatively fit with an eXciton-modified Franz-Keldysh (XFK) effect model, which includes the electric-field dependent exciton binding energy due to the quadratic Stark effect. A saturation of the spectral red-shift with reverse bias is observed exactly at the onset of dielectric breakdown providing a spectral means to detect and quantify the local electric field and dielectric breakdown behavior. Additionally, the field-dependent responsivity provides insight to the photocurrent production pathway revealing the photocurrent contributions of self-trapped excitons (STXs) and self-trapped holes (STHs). Photocurrent and p-type transport in $β-Ga_{2}O_{3}$ are quantitatively explained by field-dependent tunnel ionization of excitons and self-trapped holes. We employ a quantum mechanical model of the field-dependent tunnel ionization of STX and STH to model the non-linear field-dependence of the photocurrent amplitude. Fitting to the data, we estimate an effective mass of valence band holes $(18.8 m_{0})$ and an ultrafast self-trapping time of holes (0.045 fs). This indicates that minority-hole transport in $β-Ga_{2}O_{3}$ can only arise through tunnel ionization of STH under strong fields.
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