Kelvin force microscopy on a (Al 1-x Ga x ) 0.5 In 0.5 P light-emitting diode

Abstract

High-brightness light-emitting diodes (LED) based on AlGaInP combines the possibility to achieve high efficiency with the flexibility of tuning the emission wavelength over a large range of the visible spectrum. For optimizing the device characteristics an accurate determination of the electronic properties, like e. g. the voltage drop across the semiconductor layer sequence, is desirable. We demonstrate the potential of Kelvin Force Microscopy for quantitative investigations of the voltage drop across the heterostructure layers of an operating AlGaInP LED. The surface potential was measured for external biases between -2.0 V and +1.86 V. By subtracting the zero bias result the voltage drop could be extracted quantitatively. In the low voltage regime, most of the voltage drops in the active layer. Above +1.5 V an additional voltage drop occurs on the p-side of the device, i. e. outside the active layer sequence, which reduces the efficiency of the LED. By comparing experimental data with simulations we will discuss possible mechanisms of these findings.

Material and doping transitions in single GaAs-based nanowires probed by Kelvin probe force microscopy

“…In figure 4(a), experiments performed with different modulation voltages V AC are depicted. It is well known that increasing V AC , on the one hand, enhances the sensitivity of the measurement [13] while, on the other hand, it can have an influence on the quantitative value of the measured Kelvin voltage due to charge accumulation and/or depletion effects causing asymmetric band bending [30,31]. While for V AC = 0.5 V the contrast is obviously too low for extracting useful information, the material contrast between the Au seed particle and the semiconductor layers becomes visible for V AC 2 V. The dark spot corresponding to a low Kelvin voltage indicates the position of the Au particle at the top of the nanowire.…”