Spectral measurement of the breakdown limit of $\beta -G{a}_2{O}_3$ and tunnel ionization of self-trapped excitons and holes

Abstract

$\beta -G{a}_2{O}_3$ 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 $\beta -G{a}_2{O}_3$ 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 $(18.8m_0)$ and an ultrafast self-trapping time of holes (0.045 fs). This indicates that minority-hole transport in $\beta -G{a}_2{O}_3$ can only arise through tunnel ionization of STH under strong fields.

arXiv comment47 pages, 12 figures

References in corpus (13)

• Excitons in atomically thin transition metal dichalcogenides
• Theory of Neutral and Charged Excitons in Monolayer Transition Metal Dichalcogenides
• Dielectric screening in two-dimensional insulators: Implications for excitonic and impurity states in graphane
• Trion induced negative photoconductivity in monolayer MoS2
• Excitons in van der Waals heterostructures: The important role of dielectric screening
• High Responsivity in Molecular Beam Epitaxy (MBE) grown \b{eta}-Ga2O3 Metal Semiconductor Metal (MSM) Solar Blind Deep-UV Photodetector
• Band-to-band transitions, selection rules, effective mass and exciton binding energy parameters in monoclinic β-Ga2O3
• Dissociation of two-dimensional excitons in monolayer WSe2
• Dielectric tensor of monoclinic Ga${}_2$O${}_3$ single crystals in the spectral range $0.5-8.5$eV
• Excitonic Stark effect in MoS${}_2$ monolayers
• Stark shift of excitons and trions in two-dimensional materials
• Field-induced dissociation of two-dimensional excitons in transition-metal dichalcogenides
• Local Electric Field Measurement in GaN Diodes by exciton Franz-Keldysh Photocurrent Spectroscopy

Cited by in corpus (4)

• The anisotropic Beer-Lambert law in $\beta$-Ga${}_2$O${}_3$: Spectral and polarization dependent absorption and photoresponsivity
• Anisotropic excitonic photocurrent in $\beta$-Ga${}_2$O${}_3$
• Tailoring light holes in $\beta$-$G{a}_2{O}_3$ via Anion-Anion Antibonding Coupling
• Origin of the Anisotropic Beer-Lambert Law from Dichroism and Birefringence in $\beta$-Ga${}_2$O${}_3$