Articles you may be interested inSurface states on n-type Al 0.24 Ga 0.76 As were studied using capacitance deep-level transient spectroscopy ͑DLTS͒. Two types of hole-like traps ͑labeled as H1 and H2 in this work͒ were observed in a Al 0.24 Ga 0.76 As/In 0.22 Ga 0.78 As pseudomorphic high-electron-mobility transistor with a multifinger gate. But, no hole-like traps were observed in the fat field-effect transistor ͑FATFET͒ having a negligible ratio of the ungated surface to the total area between the source and the drain. This provides evidence that the hole-like trap peaks in the DLTS spectra originated from surface states at the ungated Al 0.24 Ga 0.76 As regions exposed between gate and source/drain electrodes. The activation energies for both surface states were determined to be 0.50Ϯ0.03 and 0.81Ϯ0.01 eV. The comparison of activation energies of the two surface states with the Schottky barrier height 0.66Ϯ0.01 eV suggests that H1 and H2 are deeply related to the Fermi energy pinning levels at the Al 0.24 Ga 0.76 As surface.