Abstract: A semiconductor light emitting device includes a light emitting structure having a first conductivity-type semiconductor layer, an active layer and a second conductivity-type semiconductor layer, a transparent electrode layer on the second conductivity-type semiconductor layer and spaced apart from an edge of the second conductivity-type semiconductor layer, a first insulating layer on the light emitting structure to cover the transparent electrode layer and including a plurality of holes connected to the transparent electrode layer, and a reflective electrode layer on the first insulating layer and connected to the transparent electrode layer through the plurality of holes.

Abstract: An example image forming apparatus includes a power device, a photosensitive drum, a transfer device to remove remaining toner based on a cleaning bias voltage, an optical sensor to detect remaining toner, and a processor to adjust the cleaning bias voltage based on a set offset bias voltage. The processor may change a surface potential of the photosensitive drum to a voltage of a set pattern using the power device, acquire a size ratio of a periodic component based on a frequency of a signal detected from the remaining toner using the optical sensor, and, based on the acquired size ratio of the periodic component being greater than or equal to a set size ratio, adjust the cleaning bias voltage based on an offset bias voltage corresponding to the size ratio of the periodic component and provide the adjusted cleaning bias voltage to the transfer device to remove remaining toner.