Evidence for voltage drops at misaligned wafer-bonded interfaces of AlGaInP light-emitting diodes by electrostatic force microscopy

Electrostatic force microscopy (EFM) with phase detection has been applied to cleaved cross sections of wafer-bonded transparent substrate (TS) AlGaIn P light-emitting diode (LED) structures. EFM was performed with the LED und er active bias to image the voltage drops across the device layers. Measure ments on a nonwafer-bonded, absorbing substrate (AS) AlGaInP LED wafer, sho wed a voltage drop only at the p-n junction. A TS wafer with high forward v oltage (Vf ) showed a much larger voltage drop at the wafer-bonded interfac e, compared with a normal TS LED wafer. Secondary ion mass spectrometry pro files of these wafers revealed similar to 1x10(13) cm(-2) of carbon at the bonded interface in the high Vf sample, compared to similar to 3x10(12) cm( -2) in the normal wafer. The unwanted voltage drop at the bonded interface was likely caused by a combination of carbon acting as a p-type dopant and the presence of interface states due to a similar to3 degrees in-plane rota tional misalignment at wafer bonding. (C) 2001 American Institute of Physic s.