Transferred charge in the active layer and EL device characteristics of TFEL cells

• Published in: Japanese Journal of Applied Physics Vol. 26; no. 9; pp. 1482 - 1492
• Main Authors: ONO, Y. A, KAWAKAMI, H, FUYAMA, M, ONISAWA, K
• Format: Journal Article
• Language: English
• Published: Tokyo Japanese journal of applied physics 01-09-1987
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Optoelectronic devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Characterization; Charge density; Hysteresis loop; Electroluminescent device; Electric charge transfer; Thin film
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/jjap.26.1482

The relationship between transferred charge in the active layer of a thin-film electroluminescent (TFEL) cell and EL device characteristics has been investigated electrically. Making use of a charge density-voltage characteristic measuring system based on a Sawyer-Tower circuit, a general formula for the input power density was found to be given by twice the product of the frequency, the threshold voltage of the active layer, and the transferred-charge density. From this formula, the luminous efficiency could be estimated, once the dependence of the luminance upon the frequency and the transferred charge density was found.
At a frequency smaller than the inverse of twice the luminous decay time,
e.g.
500 Hz in the ZnS:Mn case, the luminance was found to be proportional to the product of frequency and transferred charge density. Hence, the luminous efficiency becomes constant with a value 2–2.5 times larger than that for 5 or 1 kHz drive conditions.