GENERATION OF SELF-SUSTAINED PULSATIONS OF RADIATION IN InGaAs/GaAs/InGaP QUANTUM-WELL LASERS A. A. Afonenko, a* V. M. Stetsik, a V. Ya. Aleshkin, b V. I. Gavrilenko, b A. A. Dubinov, b S. V. Morozov, b B. N. Zvonkov, c and S. M. Nekorkin c UDC 621.378.35 We studied the dynamic characteristics of InGaAs/GaAs/InGaP quantum-well lasers generating at two wave- lengths of about 1 μm with a spectral separation of 15–40 nm. We observed experimentally regimes of jump- like switching and self-sustained pulsations of radiation. The influence of ballistic transfer of carriers during intraband absorption on the production of positive feedback in the dynamic system is studied theoretically. Key words: quantum-well semiconductor laser, self-sustained pulsation of radiation, intraband absorption, ballistic carrier transfer. Introduction. The most promising method at present for generating terahertz and far-IR radiation is consid- ered to be nonlinear generation of a difference frequency during mixing of two fields of near and middle IR ranges [1, 2]. Dual-frequency generation of radiation with wavelengths of about 1 μm and spectral separation 5–40 nm was achieved in GaAs/InGaAs/InGaP heterostructures [3, 4]. The active region of the laser structures included three quan- tum wells (QW) that differed in band gap. One narrow-band QW was located between two broad-band QWs. The wave producing layer was 0.8 μm thick; the diodes, 1 mm long and 100 μm wide. Experimental. Spectral and dynamic characteristics of the emitters were studied using pulsed pumping with a pulse length of 100–300 ns and a repeat frequency of 1–10 kHz. Spectral components of the laser radiation were iso- lated using a KSVU-23 with bandpass ∆λ < 1 nm. Emitters were separated into two basic groups according to their characteristics. Long-wavelength radiation had the minimum threshold in the first group of emitters. After exceeding the threshold of short-wavelength radiation, self-sustaining pulsations of radiation began to be generated (Fig. 1). In the second group, short-wavelength radiation had the minimum threshold. Generation was switched on using a jump re- gime. Self-sustaining pulsations of radiation arose at a certain value above the threshold current. If the threshold current was significantly exceeded, all lasers gave random radiation pulsations. The transition from quasi-regular pulsations to random ones may have been related to the multi-mode composition of the radiation from the studied lasers. Calculations. Positive feedback should occur for generation of self-sustaining radiation pulses in the system. This can arise in the laser electrical circuit because of negative differential resistance typical of laser structures with heterogeneous excitation [5]. However, negative differential resistance occurs only in a small current range near the threshold of jump-switched generation whereas the studied lasers generated pulsations at two and three times the cur- rent threshold. Positive feedback is known to arise with a saturating absorber in the laser resonator. Effective restoration of the short-wavelength radiation absorber during relaxation pulsations can be achieved during generation in the corre- sponding QW of long-wavelength radiation [6]. However, such a mechanism is evidently not realized in the studied structures because the short-wavelength radiation is mainly generated in the first transverse mode that does not interact with the central QW that amplifies the long-wavelength radiation. * To whom correspondence should be addressed. a Belarussian State University, 4 Nezavisimosti Ave., Minsk, 220030, Belarus, e-mail: afonenko@bsu.by; b Insti- tute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, Russia; c Physical Technical In- stitute of Nizhny Novgorod State University, Nizhny Novgorod, Russia. Translated from Zhurnal Prikladnoi Spektro- skopii, Vol. 74, No. 4, pp. 533–536, July–August, 2007. Original article submitted April 11, 2007. Journal of Applied Spectroscopy, Vol. 74, No. 4, 2007 0021-9037/07/7404-0589 ©2007 Springer Science+Business Media, Inc. 589