We study hot-electron cooling by acoustic and optical phonons in monolayer MoS2. The cooling power P (Pe = P/n) is investigated as a function of electron temperature Te (0-500 K) and carrier density n (10 10 -10 13 cm −2 ) taking into account all relevant electron-phonon (el-ph) couplings. We find that the cross over from acoustic phonon dominated cooling at low Te to optical phonon dominated cooling at higher Te takes place at Te ∼ 50 − 75 K. The unscreened deformation potential (DP) coupling to the TA phonon is shown to dominate P due to acoustic phonon scattering over the entire temperature and density range considered. The cooling power due to screened DP coupling to the LA phonon and screened piezoelectric (PE) coupling to the TA and LA phonons is orders of magnitude lower. In the Bloch-Grüneisen (BG) regime, P ∼ T 4 e (T 6 e ) and P ∼ n −1/2 (Pe ∼ n −3/2 ) are predicted for unscreened (screened) el-ph interaction. The cooling power due to optical phonons is dominated by zero-order DP couplings and the Fröhlich interaction, and is found to be significantly reduced by the hot-phonon effect when the phonon relaxation time due to phonon-phonon scattering is large compared to the relaxation time due to el-ph scattering. The Te and n dependence of the hot-phonon distribution function is also studied. Our results for monolayer MoS2 are compared with those in conventional two-dimensional electron gases (2DEGs) as well as monolayer and bilayer graphene.

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The theory of phonon-drag thermopower S(g) is developed in a monolayer MoS(2), considering the electron–acoustic phonon interaction via deformation potential (DP) and piezoelectric (PE) coupling, as a function of temperature T and electron concentration n(s). DP coupling of TA (LA) phonons is taken to be unscreened (screened) and PE coupling of LA and TA phonons is taken to be screened. S(g) due to DP coupling of TA phonons is found to be dominant over all other mechanisms and in the Bloch–Grüneisen regime it gives power law S(g) ~ T3. All other mechanisms give S(g) ~ T(5). These power laws are characteristic of two-dimensional (2D) phonons with linear dispersion. Screening enhances the exponent of T by 2 and strongly suppresses S(g) due to the large effective mass of the electrons. We find that S(g), due to screened DP and PE couplings is nearly the same in contrast to the results in GaAs heterojunctions. Also, we predict that S(g) ~ n(s)(-3/2), a characteristic of 2D electrons with parabolic relation. With the increasing (decreasing) T(n(s)) its exponent decreases. For comparison, we give diffusion thermopower S(d). At very low T and high n(s), S(d) ~ T and n(2)(-1). S(d) is found to be greater than S(g) for about T < 2–3 K. The results are compared with those in conventional 2D electron gas and graphene.

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