ZnO, with a large band gap (~3.37 eV) and exciton binding energy (~60 meV), is suitable for optoelectronic applications such as ultraviolet light emitting diodes (LEDs) and detectors. However, the ZnO-based p-n homojunction is not readily available because it is difficult to fabricate reproducible p-type ZnO with high hall concentration and mobility. In order to solve this problem, there have been numerous attempts to develop p-n heterojunction LEDs with ZnO as the n-type layer. Among those structures, n-ZnO/p-Si heterojunction is a good candidate due to its price competitiveness and lower driving voltage of LED. Recently, the electroluminescence (EL) of the n-ZnO/p-Si was repoted by several groups. The EL was achieved from vertical-injection ZnO-based LEDs. These structures have been attractive for high-power and high-efficiency devices. However, the LED using vertical-injection structures shows much lower extraction efficiency, because it has small top contact and large backside contact. In these structures, the injected current from the top contact enters the active region underneath the top contact. Thus, the emitted light is hindered by the opaque top contact. This problem can be solved by using a current-blocking layer (CBL) that prevents the current injection into the active region below the top contact.

In this work, the ZnO:Ga film was grown on the SiO₂-patterned p-Si (100) substrates using RF magnetron sputtering method. The SiO₂ layer was deposited to investigate the effect of the CBL. At the same time, the normal p-Si wafer was used as the substrate for the deposition of ZnO:Ga film in order to compare with the LED performance of n-ZnO:Ga/p-Si structure using the CBL. The current-voltage characteristics revealed that both LEDs showed nonlinear and rectifying behavior, although the LED using the CBL exhibited the soft turn on. On the contrary, the EL showed higher light extraction intensity in n-ZnO/p-Si LED structure with the CBL.

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