The tunable bandgap and predicted radiation resistance of the III-Nitride materials system is promising for integration into high-efficiency photovoltaic systems. The recent success of MOCVD-grown GaN/InGaN bulk and multi-quantum-well (MQW) solar cells have demonstrated that high-quality devices are achievable by this relatively mature and widely-used Nitride growth technique. While high alloy composition InGaN has been demonstrated by nitrogen plasma-assisted MBE (PAMBE), current-leakage problems have plagued vertical device structures, presumably because of group-III atom decorated threading dislocations. In contrast, record high ideality and low leakage vertical diodes have been demonstrated by NH<SUB>3</SUB>-MBE growth. By combining the benefits of high vacuum, wide temperature window, and N-rich growth environment of this technique, NH<SUB>3</SUB>-MBE will help provide valuable contributions to the development of III-Nitride photovoltaic technology. Here, we present a demonstration of high quality InGaN-based solar cell devices, which achieve performance parity with MOCVD results. GaN/InGaN/GaN P-i-N double-heterostructure solar cells were grown with 90 nm of In<SUB>0.11</SUB>Ga<SUB>0.89</SUB>N thickness and 50, 100, and 150 nm of p-GaN top-contact window layer thicknesses. Standard effusion cell sources were used for the group-III sources and dopants, while 0.2-0.5 SLM of NH<SUB>3</SUB> was used to provide the group-V. InGaN growth was performed at a calibrated optical pyrometer temperature of ~615 °C. Testing under 1-Sun AM0 broadband illumination of 0.5 mm x 0.5 mm mesa devices demonstrates excellent properties with a V<SUB>OC</SUB> of 1.75V, J<SUB>SC</SUB> of 1.11 mA/cm<SUP>2</SUP> and Fill-Factor of 73% for the 100 nm p-thickness sample. The comparison of different p-GaN thicknesses show drastically increased short wavelength spectral EQE (external quantum efficiency) for reduced p-GaN thickness, without significantly affecting the high peak EQE of greater than 55%. Because of the very high absorption coefficient (~ 10<SUP>5</SUP> cm<SUP>-1</SUP>) of GaN, it is likely that the majority of the photons with λ < 365 nm are absorbed in this p-layer and that the primary minority carrier loss mechanism responsible for low EQE in this spectral range is bulk recombination. Additionally, with optical absorption measurements in conjunction with EQE, one can decouple optical losses from carrier collection losses. By this method, an IQE (internal quantum efficiency) for the device can be extracted. Absorption was measured using a spectrometer with integrating sphere in transmission and reflection, and calculated as the difference of these from unity (Absorption(λ) = 1 – Transmission(λ) – Reflection(λ)), assuming all scattered light is captured by the integrating sphere. The comparison of average EQE data from 9 devices spanning the optical measurement region demonstrates an IQE for the InGaN region of greater than 90%.