Device Properties Study Of Blue GaN LED On Si Substrates

GaN based semiconductors manifest a wide direct band gap, and have been demonstrated a large potential for applications in Opto-electronic devices. For all these applications, the Ⅲ-Ⅴ nitride layers are usually grown on sapphire or on silicon carbide substrates. However the development of some of these applications on silicon (Si) substrates has obvious technological advantages, including the low cost, large-scale availability, good thermal and electrical conductivities and the feasibility of removing the Si substrates with wet etching. Significant mismatches in lattice constants and thermal expansion coefficients of silicon and GaN in growth process is existed , Such differences cause crack formation when the thickness of the grown film exceeds a critical thickness, which will bring in some questions about reliabilities of LED devices. consequently, It is essential to study the reliabilities of blue GaN LED on Si substrate.In this paper, Some device properties of GaN LED on Si substrates is studied, including: reliabilities, junction temperature characteristics, Ⅰ-Ⅴ characteristics and the corresponding ideality factor. some significant and innovative results is achieving as following:1. The light intensity of blue GaN LED on Si substrate doesn't decrease for three hours when the LEDs were aged in 120℃ ambience and DC 20mA operated current. in contrast,that of blue GaN LED on sapphire LED derease lightly in the same conditon ,which suggests the good reliabilities of GaN LED on Si substrate indirectly.2. The junction temperature characteristic of GaN LED on Si substrate is first reported.It is suggested that current density instead of current can be used to express the relation with the junction temperature well. Compared to the GaN LED on sapphire, it is found that the junction temperature is lower for a LED on Si substrate, which is contributed to the good thermal conductivity of Si substrate.3. The ideality factor of GaN LED on Si substrate was firstly reported.Studying the relation between the Ⅰ-Ⅴ characteristics of different samples and their crystal property, which can be decided by the Full-width at half-maximum( FWHM )of the Δω-rocking curve forGaN(102) double crystal X-ray diffraction peak, we can found that there is direct relation between the ideality factor and the crystal property: the ideality factors for different samples is 6.6 ,4.5,3.0.respectively,which is corresponding to the FWHM of each sample : 707, 530,40larcsec. We contributed the anomalously high ideality factors (n? 2.0) to the highdefect density ,which make tunneling current take place more easily.This work was supported by the National 863 nanometer project(No.2003AA302160)and electron development fund in China -...