Recent progresses in epitaxial growth and fundamental studies on electrical and optical properties of high Al-content AlGaN alloys with Si, Mg, and Zn doping are presented. For Si doped AlxGa1-xN, the Si activation energy was determined for x = 0 up to 1, and the resistivity of n-AlxGa1-xN was found to increases by one order of magnitude when Al content is increased by ∼ 8%. From photoluminescence (PL) studies, three groups of deep impurity transitions were observed, related with deep level acceptors involving cation vacancy and its complexes: (V III)3-, (VIII-complex)2, and (V III-complex)1-, which are electron traps and compensating centers. By optimizing the growth processes to reduce the densities of cation vacancy and its complexes, the n-type conductivity of AlxGa 1-xN was significantly improved. A record low room temperature n-type resistivity of 0.0075 Ω·cm has been obtained for Al 0.7Ga0.3N, and n-type conduction in pure AlN has also been achieved. We also review the electrical and optical measurement results of Mg-doped AlGaN and AlN. It was found that the overall material quality and conductivity of Mg-doped AlN are strongly correlated with the PL emission intensity of the nitrogen vacancy (VN3+) related transition. Improved conductivity was obtained by suppressing the V N3+ related emission line, which was attributed to the reduced hole compensation by VN3+. With the identification of the emission peaks associated with VN3+ hole compensating centers, the p-type conductivity of high Al-content AlGaN alloys was improved by monitoring and suppressing the intensity of the V N3+ related emission lines. P-type conduction in Al xGa1-xN (x > 0.7) was confirmed at elevated temperatures (> 700 K). The possibility of using Zn as an alternative p-type dopant was also studied. It was found that contrary to the calculation, the energy level of Zn acceptor in AlN was about 0.74 eV, which is 0.23 eV deeper than Mg level in AlN.