MOVPE growth of thick (∼1 µm) InGaN on AlN/Si substrates for InGaN/Si tandem solar cells

Abstract

In order to develop key technologies for InGaN/Si two-junction tandem solar cells, MOVPE growth of thick InGaN on Si p-on-n cell structures has been studied. By clarifying the phase separation behavior of MOVPE InGaN, a thick (>1 µm) In x Ga 1%x N (x > 0.5) without phase separation is successfully grown on AlN/Si(111) wafers. A sufficient current flow for the operation of the tandem cell is obtained through n-InGaN/AlN/p-Si structures by employing the annealing of AlN/Si wafer at around 1000°C in NH 3 flow just before InGaN growth. The annealing of AlN/Si wafers also brings about the degradation of the underlying Si pn junction. The optimization of the annealing conditions is required to balance such favorable and unfavorable effects.

Immiscibility behind the metalorganic vapor phase epitaxy of InGaN

“…In fact, the phase instability or phase separation have been observed depending on the growth temperature, composition, thickness, and growth rate. [14][15][16][17][19][20][21][22][23] In particular, at lower growth temperatures where the surface kinetics is slow enough, the apparently uniform compositions observed will be a result of the non-equilibrium "freeze-out" effect.…”

“…13 and those who followed since then. [14][15][16][17][18][19][20][21][22][23] In fact, there have been many reports on the observation of phase instability or phase separation depending on the growth temperature, composition, thickness, and growth rate. [14][15][16][17][19][20][21][22][23] The temperature range of 500 °C-800 °C, which is usually adopted for the InGaN MOVPE, must be dominated by immiscibility as it is far below the critical temperature.…”