Method and apparatus for nondestructively evaluating light-emitting materials

#This invention relates to light-emitting materials characterization or evaluation, and more specifically to the optical and electrical characterization of the electroluminescence materials which can be used for fabricating light-emitting diode (LED) or organic light-emitting diodes (OLED). Though the invention will be described with particular reference to the quantum well-based LED materials system, the invention is not so limited, and it will also find applications in optical, electrical and optoelectronic evaluation of all type light-emitting materials systems which are semiconductor-based or organic small-molecule or polymer-based, as well as p/n junction, semiconductor laser structures, and the like.

#Breakthroughs in artificial lighting from semiconductor-based or organic small-molecule- or polymer-based light-emitting materials system have led to tremendous opportunities in modern society. Solid-state lighting (SSL) based on semiconductor light-emitting diode (LED) is an emerging new-generation lighting technology which meets the worldwide trend for more energy efficient and environment-friendly usage of the finite energy. Organic small molecule and polymer-based LEDs (OLEDs) have the advantages of cost-efficiency, mechanical flexibility and large area, which offer the potential to revolutionize the flat-panel display industry, and therefore change how and where people can access the information through displays in TVs, computers and portable electronic devices. However, these lighting technologies are still too expensive for wide-spread applications. In order to reap the benefits of these exciting technologies, innovative and high-yield manufacturing equipment and tools are needed to overcome the hurdles to widespread market penetration.

#The light-emitting or luminescence from both semiconductor-based and organic small-molecule or polymer-based materials systems are produced by electrical current injection through radiative recombination of excess electrons and holes in the emissive/active layers. Correspondingly this type luminescence is usually called electroluminescence. In order to optimize the material growth recipe or control quality for further device fabrication, it is of great interest to nondestructively characterize the electroluminescence behavior of the material at the wafer level as the finished device (LED or OLED) functions through electroluminescence.

#The invention may take forms in various components and arrangements of components, and various steps and arrangements of steps. The drawings are only for the purposes of illustrating a preferred embodiment and are not to be constructed as limiting the invention.

#FIG. 1 is a schematic illustration of one embodiment of a nondestructive LED/OLED probe.

#FIG. 2 is a schematic drawing of one embodiment of electrode arrangement (hexagonal) used in FIG. 1.

#The present invention will be described with the reference to the accompanying figures wherein like reference numbers correspond to like elements.

#With reference to FIG. 1, a light-emitting material testing method is described in accordance with one embodiment of the nondestructive LED/OLED probe. The nondestructive LED/OLED probe 10 operates upon an associated light-emitting sample 20. The associated sample 20 typically has a plurality of layers 22, 24, 26 which are usually grown on a substrate 28. In FIG. 1, a gallium nitride (GaN) based LED structure is exemplarily shown, which includes a sapphire or silicon carbide (SiC) substrate 28, a p-type GaN region 22 and a n-type GaN region 26. The sandwiched layer between the p-type GaN region 22 and the n-type GaN 26 are AlInGaN (Al: aluminum, In: indium) multi-quantum-well barriers 24 which comprise the active/emissive region of LED device. Electrically the p-type GaN region 22 and the n-type GaN region 26 can be briefed as two conductive layers since they are mainly developed for anode and cathode contacts to inject the electrical current. Certainly, the invention is not limited in application to the exemplary GaN-based LED structure shown in FIG. 1, the associated sample 20 can be any type of semiconductor-based or organic small-molecule- or polymer-based light-emitting materials systems which can be used for fabricating the light-emitting diodes (LEDs) or organic light-emitting diodes (OLEDs). The invention will also find applications in characterizing p/n junction, semiconductor laser structures, and the like.

#With continuing reference to FIG. 1, the nondestructive LED/OLED probe 10 consists of electrodes 12 and 16. Well-defined electrodes 12 and 16 are used to temporarily form electrical contacts 21 and 27 to the p-type GaN. LED devices 25 and 23 are simultaneously formed in the active layer at the places right below the corresponding contacts 21 and 27, with well-defined electrode contacts define the device area. Preferably, the force of electrodes on the material is properly controlled to avoid possible mechanical damage to the tested material. One exemplary approach to control the electrode force is to use spring 14 loaded electrodes 12 and 16. Though metal probes, such as commercially available pogo probes, can be used in the present invention, the tip of electrodes 12, 16 is preferably made from an elastically-deformable electrically-conductive material and has flat surface with well-defined contact area. Together with means for controlling the electrode force, the elastically-deformable electrically-conductive material is used to ensure that intimate contacts 21 and 27 are formed between the electrodes and the light-emitting material and the areas of the temporary LED (or OLED) devices 23 and 25 are well-defined. The elastically-deformable electrically-conductive material can be a conductive elastomer or a conductive polymer.