Deep traps and persistent photocapacitance in β-(Al0.14 Ga0.86)2O3/Ga2O3 heterojunctions
Abstract
Persistent photocapacitance (PPC) was observed in β-(Al0.14Ga0.84)2O3/n+Ga2O3 heterojunctions at low temperatures. The effect is seen in capacitance-frequency measurements under illumination and in admittance spectra after illumination. In the latter case, the capacitance versus frequency curve after illumination returned to its dark values only at temperatures between 225 and 275 K. Prominent hole-trap-like peaks in optical deep level transient spectroscopy (ODLTS) near 130 K were attributed to quenching with temperature of the PPC effect. The phenomena were assigned to electrons being excited from deep traps in the (Al0.14Ga0.86)2O3 barrier into the two-dimensional electron gas (2DEG) in the Ga2O3 substrate. The reverse process then involves excitation of non-equilibrium electrons in the 2DEG back into the ternary barrier layer and subsequent re-capture by the host deep traps. The effective barrier height for this recovery process was ∼0.2 eV, as estimated from ODLTS measurements. The spectral dependence of the effect suggests the presence of deep traps with optical ionization thresholds near 1 eV and ∼2.3 eV. The shift of the threshold voltage necessary to deplete the 2DEG as a function of the photon energy during illumination at room temperature indicates that the most prominent centers in the barrier have an optical ionization energy near 2.3 eV and a sheet density of ∼1012 cm−2. In microcathodoluminescence (MCL) spectra of the heterojunction, a blue shift by 0.2 eV of the MCL band near 3.1 eV dominant in the substrate and the emergence of a weak MCL peak near 4.8 eV were observed. Electron beam induced current measurements point to the presence of small local areas where the 2DEG formation is handicapped due to Al composition variations or to defects.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 04, 2019
- Source ID
- 10.1063/1.5080941
Entities
People
- A. Y. Polyakov
- Chaker Fares
- Eugene Yakimov
- Fan Ren
- I. Shchemerov
- Jiancheng Yang
- N. B. Smirnov
- Stephen Pearton
- А. I. Kochkova
- А. В. Черных
Organizations
- Defense Threat Reduction Agency
- Ministry of Education and Science of the Russian Federation
- National University of Science and Technology
- Russian Academy of Sciences
- University of Florida