Homoepitaxial growth of (100) Si-doped β-Ga_(2)O_(3) films via MOCVD

Homoepitaxial growth of Si-doped β-Ga_(2)O_(3) films on semi-insulating(100) β-Ga_(2)O_(3) substrates by metalorganic chemical vapor deposition(MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in(100) β-Ga_(2)O_(3) films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga_(2)O_(3) film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the(400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 10~(15) – 1.74 × 10~(20) cm~(-3). Hall measurements demonstrate a high electron mobility value of 51cm~2/(V·s), corresponding to a carrier concentration of 7.19 × 10~(18) cm~(-3) and a high activation efficiency of up to 61.5%. Transmission line model(TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10~(-4) Ω·cm~2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 10~(19) cm~(-3), confirming the effective Si doing in the MOCVD epitaxy.

Influence of Nd^(3+) concentration on mid-infrared emission in PbF_(2) crystal co-doped with Ho^(3+) and Nd^(3+) ions

A promising series of Ho_(y)Nd_(x)Pb_((1-x-y))F_2(x = 0, 0.01, 0.02, 0.03, 0.04;y = 0.02) crystals was grown by the Bridgman method. The influence of the Nd^(3+)ions concentration on mid-infrared(~2.0, ~2.9 and ~3.9 μm)fluorescence emissions of Ho^(3+)ions in the PbF_(2) crystal excited by 808 nm laser diode was investigated in this work. The energy transfer mechanism between Nd^(3+)ions and Ho~(3+)ions under different concentrations of the Nd^(3+)ions was systematically analyzed. The results show that the Nd^(3+)ions have good sensitization and deactivation effect on the Ho^(3+)ions to stimulate the mid-infrared fluorescence emissions. The experimental analysis proves that the sensitization efficiency of the Nd^(3+)ions is relatively stable at around 93.45% with varying Nd^(3+)-doping concentrations. Concentration dependence studies indicate that the concentration of the Nd^(3+)ions has significant influence on mid-infrared emissions.When the doping concentration of the Nd^(3+)ions is up to 2.0 at%, the intensity of ~2.0, ~2.9 and ~3.9 μm emissions all reach the maximum. The output characteristics of a 3.9 μm laser are simulated, and it is found that with the increase of the Nd^(3+)-doping concentration, the peak power, pulse width, and peak energy all meet the trend of first increasing and then decreasing, and Ho_(0.02)Nd_(0.02)Pb_(0.96)F_(2) crystal displays the best performance. All the results show that the Nd^(3+)/Ho^(3+)co-doped PbF_(2) crystals might act as a useful optical medium for mid-infrared laser applications.