Laser Spike Annealing (LSA) is a powerful technique for investigating reaction kinetics at high temperatures in the sub-millisecond time regime. In this regime, significant advantages have been shown in applications of ultra-shallow junction formation in ion-implanted III–V and III–N semiconductor materials. Dopant activation of Si-doped InGaAs and GaN heterostructure was studied using CO2 and laser diode annealing in sub-millisecond and millisecond timescale. Under LSA, the activation of high–dose implanted dopants was increased in both InGaAs and GaN to peak concentrations comparable (>80%) to the as-implanted dose. During laser annealing, thermodynamic limits were also approached including materials decomposition and damage, which ultimately limited full characterization of the activation behaviors. To better understand the annealing windows, we developed an in–situ characterization technique which matches well with laser annealing for combinatorial and high–throughput characterization; this capability significantly enhances the characterization kinetic dopant activation limitations of III–V and III–N materials. A complementary approach for temperature profiling of LSA was also developed using a thermoreflectance imaging technique. The temperature dependence of reflectance at short wavelengths was used to determine the in-situ dynamic temperatures during CO2 LSA. Temperatures were calibrated using optical functions of bulk Si with effects of black-body radiation emission captured at longer wavelengths. Thermoreflectance imaging results were compared with previous results, and show good agreements with direct Pt thermistor measurements and simulations results in both space and time. In the future, thermoreflectance imaging can be exploited to understand not only impurity interaction in III–V and III–N materials, but also to explore kinetics and phase transformations in metastable materials.