2006 Fiscal Year Final Research Report Summary
Study of degradation mechanism and its control on II-VI, III-V wide bandgap light emitting device
| Project/Area Number |
16360008
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Applied materials science/Crystal engineering
|
|---|
| Research Institution | Tottori University |
|---|
Principal Investigator |
ANDO Koshi Tottori University, Faculty of Engineering, Professor, 工学部, 教授 (60263480)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
ISHII Akira Tottori University, Faculty of Engineering, Professor, 工学部, 教授 (70183001)
ABE Tomoki Tottori University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (20294340)
MATSUOKA Takashi Tohoku University, Institute for Materials Research, Professor, 金属材料研究所, 教授 (40393730)
|
|---|
| Project Period (FY) |
2004 – 2006
|
| Keywords | widedgap semiconductor optical device / degaradation of white LED / thermal and electronic defect reaction / REDR effect / generation of microscopic point defects / artificial control of defect genearation / long lived white LEDs |
|---|
| Research Abstract |
In this term we have performed precise and systematic device aging-tests together with analysis of microscopic point defect reaction under device operation condition. Main results obtained are summarized as follows :
[1] Device degradation mechanism of ZnSSe widgap LEDs and LDs (Forward Biased Operation).
Slow-Mode degradation mechanism of ZnSe white LEDs and blue LDs has appeared during long period devic operation condition (1000-10000 hrs). This degradation mode is found to attribute to gradual carrier removal effect in p type cladding layer of white LED and blue-LDs. The reduction in the carrier (hole) concentration is induced by generation of deep compensating donors in p type region very close to active QW layer. Driving force of deep-donor generation is not from pure thermal effect, but from vicious electronic excitation effect (REDR effect : nonradiative e-h recombination enhanced defect reaction process with high-density multi-phonon emission). This degradation mode (REDR mode) i
… More
s found to be a typical degradation process of long lived LED and LDs of widgap semiconductors as ZnSe, ZnO and GaN. One effective LED structure for improving this is to form "double cladding structure" on p-type region (cladding and guiding layer), and in fact this device structure is verified to act as useful one for long lived ZnSe white LEDs (> 10000 hrs operation).
[2] Degradation of ZnSSe and GaN PIN and APD devises (Reverse Biased Operation) :
Device aging tests of ZnSSe and GaN photodiodes (PIN and APD) are perormed under reverse biased (high electric field condition) operation conditions. Inn this experiment generation of microscopic point defects in high field region is monitored by in-situ DLTS (ICTS) measurements. Important insights on this study are (a) no detectable generation of point defects can be seen in both ZnSe-and GaN photodiodes, and (b) long device operation (>10000 hrs) can be established by using optimum device fabrication processes. This important results indicate that high electric field does not cause any defect reaction in widegap semiconductor photodiode devices.
[3] New Defect Control Technique for long lived LEDs of Widegap Semiconductors
Based on fundamental defect reaction study during this research project (2004-2006), we have found one effective control method (current injection pulse width control) of bright and long lived white LED operation. The point of this technique is to control of microscopic defect generation by adjusting current pulse width. Note here that pulse duty-ratio control (for thermal effect) is no meaning for long lived widegap light emitting devices To confirm the validity of this technique we have made detailed aging experiment with changing current pulse-width(Δw=m sec -- nano sec.), together with monitoring microscopic point defect reaction. Using the pulse-width controlling technique in high quality ZnSe white LED, we have demonstrated long lived operation (>20000 hour : 25 lm/W (averaged value). In addition it is confirmed that this new technology is more effective for bright and extremely long lived GaN white LEDs. Less
|
