A comparison of deep level effects on the DC characteristics of In xGa1-xP/In0.20Ga0.80As/GaAs and Al0.24Ga0.76As/In0.20Ga0.80 As/GaAs high electron mobility transisto

Deep Level Transient Spectroscopy (DLTS) has been used to characterise the deep levels in In_xGa_1-xP/In_0.20Ga_0.80 As/GaAs (0.40⩽x⩽0.48) pseudomorphic high electron mobility transistors (pHEMT) grown by solid source molecular beam epitaxy (SSMBE). Three different pHEMT devices were investigated, with a single InGaP barrier layer, double InGaP barrier layers and strained InGaP barrier layers. Only one electron trap in the InGaP barrier layer was detected in each of the devices. The activation energy of the electron trap is 0.39 eV for the single barrier layer device, 0.40 eV for the double barrier layer device and 0.57 eV for the strained barrier layer device. The trap concentrations are 7.22×10¹⁸ cm^-3 , 2.38×10²⁰ cm^-3 and 5.02×10²⁰ cm^-3, respectively. The current-voltage (I-V) characteristics and transconductance of the devices were measured at 300 K, 77 K and 30 K. The drain saturation current becomes smaller due to the carriers being captured by the defects, and the transconductance becomes higher due to an increase in carrier mobility in the channel as the temperature was lowered from 300 K to 30 K. No devices showed any collapse in the I-V characteristic or persistent photoconductivity (PPC) at low temperature, suggesting that the trap in the InGaP layer does not have a DX centre-like characteristic. A comparison was made with Al_0.24Ga_0.76 As/In_0.20Ga_0.80As/GaAs pHEMTs. Only one electron trap was detected in the Al_0.24Ga_0.76As layers of the latter pHEMTs. The trap concentration is 1.72×10²⁰cm^-3. Drain current collapse at temperature below 77 K at low drain bias and persistent photoconductivity (PPC) effect were evident, indicating the presence of DX centers in the Al_0.24Ga_0.76As layers