Study of Laser Threshold Temperature Sensitivity in Optically Pumped GaN Epilayers

Abstract

PACS : 78.20.Bh; 78.66.Fd On the base of experimental spontaneous emission spectra measured at laser threshold the temperature dependencies of the radiative R sp and nonradiative Q recombination rates as well as the spontaneous emission internal quantum efficiency h sp for optically pumped wurtzite GaN=Al 2 O 3 epilayers have been calculated. The recombination rate induced by the amplified luminescence R lum was taken into account. It is shown that the main reason of the increasing threshold pump rate R p with temperature T for the GaN-based compounds is a substantial rise of the nonradiative recombination rate. The portion of Q in R p exceeds 80-90%. The contributions of R sp and R lum in R p amount to several percents. The h sp value is of 0.12-0.18 within the temperature interval of 300-450 K. Further increase in T leads to an abrupt decrease in h sp down to 0.06 at 517 K.

Interband transition matrix element and temperature dependence of the lasing threshold for GaN laser structures

“…Some mismatch between the simulated and experimental curves on the long-wavelength wing of W sp (E) is explained by the effect of impurity states and enhancement of luminescence on the recombination processes. The contribution of enhanced luminescence to the recombination rate for the studied samples is not more than a few percent [5].…”

“…This includes in particular the phenomenon of the rapid rise in the threshold pump rate R p of epitaxial GaN laser structures as the temperature T of the medium increases above some critical value T b [4]. As shown in [5,6], this type of variation in R p (T) is mainly explained by the features of the temperature variation of the radiative (R sp ) and nonradiative (Q) recombination rates. However, this approach gives only general ideas about the possible reason for the strong temperature dependence of the lasing threshold in GaN semiconductor lasers.…”

“…The spontaneous emission spectra of GaN epitaxial layers, recorded in relative units at the lasing threshold, are adjusted to absolute units by the procedure presented in [5,10]. Figure 1 shows the dependences of the luminescence power W sp on photon energy E obtained in this way for the studied GaN laser structures at different temperatures T.…”

“…Researchers have directed significant efforts toward design of high-efficiency laser structures emitting in the blue region of the spectrum at elevated temperatures of the active medium [1][2][3]. Today the optical properties of such structures are being intensively studied [4][5][6][7][8][9]. Nevertheless, many physical processes observed in the active layers of GaN-based emitters remain insufficiently studied.…”

“…1 by a focused beam from a nitrogen laser. The luminescence (spontaneous emission) spectra and the laser emission spectra were recorded in the temperature interval 300 K to 517 K. A more detailed description of the experimental conditions is given in [5,6].…”