Measurement of surface contact potential of AlGaN/GaN heterostructure and n‐GaN by Kelvin probe force microscopy

Abstract

The contact potential images of the AlGaN/GaN heterostructure and n-GaN before and after thermal treatment have been successfully obtained by Kelvin probe force microscopy (KFM). It was found that the removal of the surface potential shielding effect of the adsorbed water-related layer by means of thermal treatment was effective in the observation of low potential regions at around the dislocations. The low potential regions at dislocations indicated that the dislocations of AlGaN/GaN heterostructure and n-GaN were negatively charged. The contact potential variations around the dislocations in AlGaN/GaN heterostructure was much larger than that of n-GaN in both magnitude and diameter.

Kelvin Probe Force Microscopy under Variable Illumination: A Novel Technique To Unveil Charge Carrier Dynamics in GaN

“…By comparing the CPD map to the topography, we can see that dislocation pits are located in areas with higher CPD (between 150 and 200 mV difference), which, in our setup, means more positively charged regions. This finding differs from previous studies, which observed/predicted negatively charged dislocations. − However, these negative fixed charges at dislocations are not seen in every sample: some studies measured no charge density on TDs, , and others reported even positively charged dislocations. − KPFM is sensitive to the surface states and, therefore, to any possible contamination layer (oxide, carbon complexes, adsorbed water, etc. ), which, in turn, depends on the growth process, the cleaning process, if any, and the time and conditions of storage, making the comparison of samples difficult.…”

“…This finding differs from previous studies, which observed/predicted negatively charged dislocations. 23−29 However, these negative fixed charges at dislocations are not seen in every sample: some studies measured no charge density on TDs, 30,31 and others reported even positively charged dislocations. 32−34 KPFM is sensitive to the surface states and, therefore, to any possible contamination layer (oxide, carbon complexes, adsorbed water, etc.…”

“…Additionally, we submitted the sample to a surface treatment (heated at 220 °C for 1 h in UHV) in order to get rid of possible surface states, most likely adsorbed water. ,, The XPS measurements after heating (following the same heating procedure under standard vacuum) reveal a decrease in the O 1s line, from 29.2% before heating to 25.8% after heating (Figure S2b), and an increase in the C 1s line, from 44.0% before heating to 46.5% after heating (Figure S2c). Although the total percentage of carbon slightly increases, which may be due to degassing of the sample holder during heating, the C 1s peak associated with oxygen bonding decreases (see Figure S2c).…”

Impact of $\hbox{N}_{2}$ Plasma Power Discharge on AlGaN/GaN HEMT Performance

“…There are difficulties in extracting accurate surface potential values, particularly due to the humidity level in the atmosphere during the measurement [23]. Nevertheless, qualitative and quantitative trends for surface potential main values were inferred.…”