Internal efficiency of semiconductor lasers with a quantum-confined active region

Abstract

Abstract-We discuss in detail a new mechanism of nonlinearity of the light-current characteristic (LCC) in heterostructure lasers with reduced-dimensionality active regions, such as quantum wells (QWs), quantum wires (QWRs), and quantum dots (QDs). It arises from: 1) noninstantaneous carrier capture into the quantum-confined active region and 2) nonlinear (in the carrier density) recombination rate outside the active region. Because of 1), the carrier density outside the active region rises with injection current, even above threshold, and because of 2), the useful fraction of current (that ends up as output light) decreases. We derive a universal closed-form expression for the internal differential quantum efficiency int that holds true for QD, QWR, and QW lasers. This expression directly relates the power and threshold characteristics. The key parameter, controlling int and limiting both the output power and the LCC linearity, is the ratio of the threshold values of the recombination current outside the active region to the carrier capture current into the active region. Analysis of the LCC shape is shown to provide a method for revealing the dominant recombination channel outside the active region. A critical dependence of the power characteristics on the laser structure parameters is revealed. While the new mechanism and our formal expressions describing it are universal, we illustrate it by detailed exemplary calculations specific to QD lasers. These calculations suggest a clear path for improvement of their power characteristics. In properly optimized QD lasers, the LCC is linear and the internal quantum efficiency is close to unity up to very high injection-current densities (15 kA/cm 2 ). Output powers in excess of 10 W at int higher than 95% are shown to be attainable in broad-area devices. Our results indicate that QD lasers may possess an advantage for high-power applications.Index Terms-Quantum dots (QDs), quantum wells (QWs), quantum wires (QWRs), semiconductor heterojunctions, semiconductor lasers.

Optical power of semiconductor lasers with a low-dimensional active region

“…It is the capture velocity (measured in cm=s), which is a proper parameter describing the carrier capture into a QW. [6][7][8][9][10][11][14][15][16] The thermal escape time and the capture velocity are related to each other (see Ref. 16 for the general expression relating s n;p;esc and v n;p; capt;0 ).…”

“…1,2 Among them is the carrier capture from a bulk reservoir region [optical confinement layer (OCL)] into a low-dimensional active region. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] Analytical models can provide insights into these processes and be used to optimize the laser structures to achieve desired operating characteristics. To develop analytical approaches, certain assumptions and simplifications should be made.…”

Light-current characteristic of a quantum well laser with asymmetric barrier layers

“…The increase of n OCL with j is due to noninstantaneous capture of carriers from the OCL into the quantum-confined active region, 11,12 …”

“…It also leads to sublinearity of the light-current characteristic (LCC) in such lasers. 11,12 In Refs. 13 and 14, to suppress bipolar population and hence electron-hole recombination outside QDs, tunnelinginjection of both electrons and holes into QDs from two separate QWs (one on each side of the QD layer) was proposed.…”

Direct and indirect capture of carriers into the lasing ground state and the light-current characteristic of quantum dot lasers

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In Refs. [19][20][21], the lightcurrent characteristic (LCC) of semiconductor lasers (the optical power as a function of the pump current) was calculated considering only direct capture of carriers from the optical confinement layer (OCL) into the lasing state in a quantum-confined active region. In Ref.…”