AIGaN/GaN high electron mobility transistors (HEMTs) have been developed for current-collapse-free operation at high drain bias voltages. The newly designed single-chip GaN H E W amplifier for W-CDMA h e station applications achieves a record CW output power of 150 W with a high power-added efficiency (F'AE) of 54% at 2.1 GHz. The amplifier, combined with a digital pre-distortion (DPD) system, also demonstrates a state of the art efficiency of 40% with an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4 4 e i W-CDMA signals and reaches the saturated peak power level of 174 W with a drain supply voltage of 63 V. We prove for the first time that the AIGaN/GaN HEMT amplifier can completely fulfills the W-CDMA system requirement.

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We investigated photoionization of deep traps in AlGaAs/GaAs multiple-quantum-well layers and measured the photocurrent (PC) parallel to the layers under a small electric field. There is a small shoulder due to the photoionization of a deep trap on the low-energy side of the n=1 exciton resonance peak in the PC spectra taken as a function of the excitation energy ℏω. The excitation energy dependence f(ℏω) and amplitude A of the photoionization cross section, σ(ℏω)=Af(ℏω), are determined by the time constants of single-shot PC transients. The excitation energy dependence increases linearly with excitation energy. The photoionization threshold energy EMQWth and the amplitude A increase as well thickness decreases. These characteristics are explained well by our theoretical study on the photoionization of a deep trap to subbands.

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A theoretical crystal-field model for the X-(X = 0, S) centres with U,-symmetry leads to three equivalent operators for the np' 'P ground state, from which the g tensor of the defects can be calculated analytically. Three equivalent operator coefficients p , q , r a r e fitted to four a priori independent experimental quantities g,,, g",, gzz and q . This leads to an excellent agreement for NaCl: S-, RbCl : 0-and KCI : 0 -, and to a fair agreement for KCI : S -.