Wang Jinbin

An Improvement on the Junction Temperature Measurement of Light-Emitting Diodes by using the Peak Shift Method Compared with the Forward Voltage Method

The junction temperature of red, green and blue high power light emitting diodes (LEDs) is measured by using the emission peak shift method and the forward voltage method. Both the emission peak shift and the forward voltage decrease show a linear relationship relative to junction temperature. The linear coefficients of the red, green and blue LEDs for the peak shift method and the forward voltage method range from 0.03 to 0.15 nm/°C and from 1.33 to 3.59 mV/°C, respectively. Compared with the forward voltage method, the peak shift method is almost independent of bias current and sample difference. The variation of the slopes is less than 2% for the peak shift method and larger than 30% for the forward voltage method, when the LEDs are driven by different bias currents. It is indicated that the peak shift method gives better stability than the forward voltage method under different LED working conditions.

Electronic structure and magnetic properties of (Mn, N)-codoped ZnO

The electronic structures and magnetic properties of (Mn, N)-codoped ZnO are investigated by using the first-principles calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn2+ ion transfers to the N2− ion, which leads to the high-state Mn ions (close to +2.5) and trivalent N3− ions. In an antiferromagnetic state, one electron transfers to the N2− ion from the downspin Mn2+ ion, while no electron transfer occurs for the upspin Mn2+ ion. The (Mn, N)-codoped ZnO system shows ferromagnetism, which is attributed to the hybridization between Mn 3d and N 2p orbitals.

A KINETIC MODEL FOR THE INITIAL GROWTH OF DIAMOND FILMS

Based on a surface reaction mechanism for diamond deposition from the gas phase, a kinetic model is developed to describe diamond nucleation sites and the initial stage of diamond growth in chemical vapor deposition. The time-independent solutions to the rate equations, which describe the steady-state growth of diamond films, is obtained analytically for the case of small ratio of carbon flux to atomic hydrogen flux. The time-dependent solutions obtained by numerical methods for large ratio of carbon to atomic hydrogen flux describe the nucleation and initial gorwth stage of diamond films. This model suggests some general predictions for diamond nucleation and growth and can be used to explain several important experimental phenomena observed by others.