The photoemission and injection properties of two GaAs/(Al,Ga)As electrodes with effective negative electron affinity (NEA) are studied in the parallel-plate capacitorlike vacuum photodiode. Both electrodes are bonded to the glass of the input windows, allowing measuring the quantum yield in the transmission and reflection modes. The photodiode with NEA states of both electrodes is sensitive to the illumination in the 400-900 nm range and produces the photocurrent with no bias applied between electrodes. The energy distribution of emitted electrons is studied as a function of the transverse energy component to the surface in the temperature range of 20-300 K. The presence of the fine structure in the photoemission spectra is associated with the electron-phonon coupling in two-dimensional quantized states in the band-bending region. The two-electrode vacuum photoemission system demonstrates the negative differential conductivity. The cathodoluminescence signal is measured as a function of free-electron injection energy with the threshold appearance less than 0.05 V between electrodes.